Due Diligence and the US Defend
Forward Cyber Strategy
ERIC TALBOT JENSEN AND SEAN WATTS 

Aegis Series Paper No. 2006

Introduction
As its name implies, the 2018 US Department of Defense (DoD) Defend Forward
strategy is principally reactive.1 The strategy assumes that the United States will
continue to suffer harm from competitors and malign actors through cyberspace.
Accordingly, it outlines US reactions in order to preempt threats, defeat ongoing
harm, and deter future harm.2 Previous strategies have instructed similarly, but
the 2018 National Cyber Strategy purports to reflect a strategic evolution in its
overt commitment to countering cyber harm at its origin and to doing so not
intermittently or episodically but on a “day-to-day” basis.3 Defending forward
involves a wide range of cyber activities, but a defining feature will likely be routine
nonconsensual cyber operations in the networks of hostile foreign governments and
private actors.
These operations are sure to require technical, doctrinal, political, and even
diplomatic reevaluations. But they also call for review of supporting international legal
justifications. While a host of international law doctrines will be relevant to Defend
Forward, the principle of due diligence is likely to play a significant role, in light of
both the reactive nature of Defend Forward and the interconnected yet shadowy
domain of cyberspace.
Well before the Defend Forward strategy or even cyberspace itself emerged, states
developed the international law obligation of due diligence as an important
regulation of international relations. In the incomplete and fragmented international
legal system, due diligence has served as a general policing regime to manage and
redress harm between states. At its most general level, due diligence requires states
to take reasonable measures to put a stop to activities, whether private or public,
within their borders that cause serious adverse consequences to other states.4
International tribunals and publicists have repeatedly confirmed that breaches of
due diligence entitle injured states to relief and reparations from offending states. Just
as important, breaches of due diligence authorize victim states to react with a wide
range of measures of self-correction from nondiligent states, including resorting to
countermeasures.5

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In these respects, breaches of due diligence resemble other international wrongs
that give rise to self-help. Breaches of due diligence are distinct, however, in that
wrongfulness arises not from attribution of harm to organs or agents of the offending
state but rather from the emanation of harm itself. A victim state can establish a
breach of due diligence without establishing the territorial state’s responsibility for
the harm; the victim state need only determine that the offending state knew of
and failed to quell harm coming from its territory. In this respect, breaches of due
diligence most often involve omissions rather than affirmative acts by states. Alleged
breaches of due diligence can potentially justify reactive measures of self-help such
as those envisioned by the Defend Forward strategy, particularly in situations where
cyber harm emanates from another state’s territory but cannot be attributed directly
to that state.6
Despite the doctrine’s potential utility in curbing harmful omissions by states and
justifying remedial measures, due diligence remains an ambiguous concept in
international law. Some detect reluctance on the part of states, including the United
States, to publicly support or clarify the concept of due diligence.7 Others question
whether due diligence is a freestanding obligation at all, perceiving it instead as
a secondary rule that merely informs the implementation of other primary rules
of conduct.8 It is also unclear whether the duty of due diligence extends to an
obligation to monitor and prevent harm ex ante. Moreover, the precise threshold
or degree of harm required to establish a breach remains unsettled. Adding
complexity, the concept of due diligence has developed to include regime-specific
standards and duties applicable to various domains and conditions of international
relations.
This essay evaluates perceived US hesitance concerning due diligence in light of the
Defend Forward cyber strategy. We begin with a brief review of due diligence as an
obligation of general international law. We highlight a broad base of support from
international tribunals and commentators for due diligence as a freestanding rule
of conduct. We then recount recent efforts to apply due diligence to activities in
cyberspace. Next, we review past US foreign relations experience with due diligence,
including its invocation in international litigation and its use to generate favorable
diplomatic outcomes. We conclude that positive US diplomatic and legal precedent
counsel in favor of renewed recognition of due diligence as an obligation under
general international law. We then examine how conceptions of due diligence may
complement the Defend Forward strategy in cyberspace. Specifically, we suggest how
the United States might best tailor a view on due diligence specific to activities in
cyberspace and offer doctrinal refinements that might be acknowledged in light of the
US Defend Forward strategy.

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Due Diligence in International Law
General Due Diligence
A state’s obligation not to permit activities within its territory that harm other states
finds classic international legal expression in the phrase sic utere tuo et alienum non
laedas (use your own property in such a manner as not to injure that of another).9 By
the late nineteenth century, influential commentators had begun to refine the no harm
maxim into a concept of due diligence. In 1871, the former British Majesty’s advocate
Robert Phillimore observed, “[a] Government may by knowledge and sufferance, as well
as by direct permission, become responsible for the acts of subjects whom it does not
prevent from the commission of an injury to a foreign State.”10 Although Phillimore’s
formulation suggests a theory of liability as much as one of international wrong,
later publicists, including Lassa Oppenheim and Hersch Lauterpacht, soon translated
the concept into an international obligation of conduct. Oppenheim identified
“international delinquency,” in the form of “culpable negligence” resulting in injury
to another state, as a violation of general international law.11 Meanwhile, Lauterpacht
endorsed notions of due diligence as means by which to hold a “defaulting State to the
possible consequences of its negligence.”12
By the mid-twentieth century, states increasingly invoked due diligence in diplomatic
practice and litigation.13 Modern recitations of the obligation most often cite the
1949 International Court of Justice (ICJ) decision in the Corfu Channel case. After two
of its destroyers lawfully present in Albanian waters struck naval mines, the United
Kingdom alleged that Albania had wrongfully failed to honor its legal duty to alert
the ships to the presence of the mines. The United Kingdom framed Albania’s failure
as a breach of international law specifically addressed to maritime mines. But UK
advocates also characterized the Albanian omission as a breach of “general principles
of international law.”14
Although the ICJ could not attribute the placement of the mines to Albania, the
court held that Albania must have been aware of the mines and affirmed the United
Kingdom’s claim with respect to due diligence as a principle of international law.
Offering the clearest and now most recited expression of due diligence, the court
confirmed “every State’s obligation not to allow knowingly its territory to be used for
acts contrary to the rights of other States.”15
The court’s statement on due diligence as a matter of general international law has
been criticized as obiter dictum. Some suggest that the court should have decided the
case on the narrower legal grounds of a breach of the international law applicable to
naval mines.16 True, states had developed specific international law to govern naval
mines by the time of the Corfu Channel case. For example, the Hague Convention VIII
of 1907 required states to take “every possible precaution” to render mines harmless

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and to notify ship owners of the presence of mines off their coasts.17 But as both the
judgment of the court and the dissent observed, the Hague Convention and its regime
of precaution and notice applied only during war between state parties.18 The United
Kingdom and Albania were not at war, nor was Albania a party to the convention. As
a result, the general duty of diligence cited by the court and alleged by the UK filings
was inescapably before the court.
Two recent ICJ cases have confirmed the Corfu Channel court’s observation on due
diligence. In the Pulp Mills case, Argentina alleged Uruguay’s construction of a pulp
mill along a shared river breached both a treaty obligation to prevent harm along the
river as well as the latter’s duty of due diligence. In its judgment, the court clearly
embraced due diligence as a matter of general international law.19 Although the case
implicated a treaty specifically addressed to the situation between the parties, the
court observed, regarding general international law: “[T]he principle of prevention, as
a customary rule, has its origins in the due diligence that is required of a State in its
territory. It is ‘every State’s obligation not to allow knowingly its territory to be used for
acts contrary to the rights of other States.’ ”20
Just five years later, the ICJ revisited due diligence in the Border Area case.21 The
case arose from cross claims between Costa Rica and Nicaragua related to dredging
and road construction, respectively, along the San Juan River. Each side cited
the international law principle of due diligence as well as specific duties under
international environmental law. In its judgment, the court reiterated its Pulp Mills
conclusions on law, reemphasizing that due diligence is a general international law
principle and confirming its application to international environmental claims.
Two important points concerning the present state of due diligence can be drawn from
these ICJ cases. First, the filings of the several states party to each case demonstrate
clear support for the notion of due diligence both in a general international legal
sense and in specific contexts of international relations involving transboundary
harm. No states party to any of the three cases, nor any justice hearing them, rejected
due diligence as either an international legal principle or as a regime-specific rule of
conduct. Second, in the two more recent cases, the court not only reaffirmed earlier
observations concerning a general duty of due diligence. It also discerned refinements
to the duty, most obviously in the form of a duty not merely to suppress ongoing harm
but also to prevent it.
Yet significant uncertainty surrounds the obligation of due diligence both as a
principle of general international law and in the specific contexts in which it operates
as a separate rule. Private organizations and scholars have attempted to elicit greater
state attention to these ambiguities. On the heels of the Pulp Mills judgment, during
proceedings in the Border Area litigation, and in response to growing academic

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and diplomatic attention to the principle of due diligence, the International Law
Association (ILA) commissioned a study group “to consider the extent to which there
is a commonality of understanding between the distinctive areas of international
law in which the concept of due diligence is applied.”22 In a pair of reports, the ILA
noted s­ ector-specific iterations of due diligence alongside an “overarching concept of
increasing[] relevance in international law.”23 Still, the reports concluded further work
was necessary to refine the principle of due diligence and its numerous sector-specific
variations.

Cyber Due Diligence
The ILA’s conclusion that a “broad principle of due diligence can be understood
as underlying more specific rules of due diligence” invites consideration of how
due diligence might be applied in the rapidly developing domain of cyberspace.24
Beginning in 2004, the United Nations (UN) General Assembly convened the Group
of Governmental Experts (GGE) to discuss “Developments in the Field of Information
and Telecommunications in the Context of International Security.” Over time,
the GGE has become the leading forum for states to debate, develop, and confirm
international regulations and norms of conduct in cyberspace.25
In addition to issuing a number of important consensus declarations, including
a determination that “[i]nternational law, and in particular the Charter of the
United Nations, is applicable and is essential to maintaining peace and stability and
promoting an open, secure, peaceful and accessible ICT environment,” the GGE has
commented on the application of due diligence to the cyber domain.26 In its most
recent consensus document, issued in 2015, the GGE adopted “recommendations
for consideration by states for voluntary, non-binding norms, rules or principles of
responsible behaviour of states aimed at promoting an open, secure, stable, accessible
and peaceful ICT environment.”27 Among those recommendations was the observation
that “states should not knowingly allow their territory to be used for internationally
wrongful acts using ICTs.”28 This clear recitation of the Corfu Channel case’s notion
of general due diligence stands as a prominent, if aspirational, reference to cyber due
diligence.
Other multistate organizations have more clearly endorsed cyber due diligence as an
international legal matter. Most recently, the European Council published a statement
concerning “malicious cyber activities exploiting the coronavirus pandemic.”29 The
statement noted:
The European Union and its Member states call upon every country to exercise due
diligence and take appropriate actions against actors conducting such activities
from its territory, consistent with international law and the 2010, 2013 and 2015

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consensus reports of the United Nations Groups of Governmental Experts (UNGGEs)
in the field of Information and Telecommunications in the Context of International
Security.30

Professor Duncan Hollis has also collected views of states on cyber due diligence under
the auspices of the Organization of American States in a report titled International
Law and State Cyber Operations: Improving Transparency (Fourth Report).31 Professor
Hollis found that Chile, Ecuador, Guatemala, Guyana, and Peru have all agreed that
due diligence applies to cyber operations, with Bolivia somewhat more equivocal in
its approach.32 Meanwhile, France, the Netherlands, and Estonia have also expressed
support for the obligation of cyber due diligence in detailed public statements.33
Private commentators echo these views. For example, the authors of the 2017 Tallinn
Manual on the International Law Applicable to Cyber Operations note that “[the] due
diligence principle has long been reflected in jurisprudence [and] it is a general
principle that has been particularized in specialized regimes of international law.”34
The group further agreed that “[a] State must exercise due diligence in not allowing its
territory, or territory or cyber infrastructure under its governmental control, to be used
for cyber operations that affect the rights of, and produce serious adverse consequences
for, other States.”35
The willingness of select states, international organizations, and private commentators
to extract from international law a rule on cyber due diligence seems indicative of
trends respecting due diligence in other domains of international relations. However,
there are signs of dissent as well. After his survey of views, including those of states
that expressed positive views, Professor Hollis concluded that “there are competing
views on whether due diligence is a requirement of international law in cyberspace,”
and there is not yet a consensus among states on how the due diligence principle
will apply in the sector-specific area of cyber operations.36 Thus, despite more than
a century of repeated confirmation by accepted sources of international law, there
remain signs that some states harbor reservations about due diligence and how, if at
all, the principle applies to cyberspace.

US Approaches to Due Diligence
The United States and General Due Diligence
The United States played a conspicuous role in the early development of due diligence
as a principle of international law. From the mid-nineteenth century to the midtwentieth century, the United States was involved in three prominent disputes
involving early conceptions of the duty of due diligence. In this same period, the
US Supreme Court accepted international law notions of due diligence as well. In

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each case, the US government cited or acknowledged breach of due diligence as a
freestanding cause of action or international law obligation. Yet today, the US position
on due diligence is unclear. In his report, Professor Hollis evaluated US legal policy
toward due diligence specifically. He surmised:
[T]he United States has tended to describe any obligations to respond to requests
for assistance in non-binding terms. The lack of any public US endorsement of due
diligence as a legal rule in either the GGE context or elsewhere may be indicative of
US doubts as to its legal status.37

This recent US hesitance with respect to due diligence warrants a review of US
diplomatic practice and outcomes relating to the concept.
The US experience with due diligence extends to the early days of the republic. In
1837, during an insurrection in Canada against the British, Canadian rebels hired
a US-flagged steamer, the Caroline, to deliver supplies from the United States across
the Niagara River. Unsatisfied with the response to its complaints about the United
States’ failure to stem the flow of supplies to the Canadian rebels, Great Britain took
matters into its own hands and destroyed the Caroline.38 The incident generated a now
famous legal correspondence between the US government and Great Britain. Because
the Canadian rebels had not met the conditions of belligerency, the United States had
not declared itself to be a neutral party and therefore did not incur the obligations a
neutral state owes to belligerents in a conflict. Thus the United States’ failure to cut
off rebel supply chains could not be characterized as a breach of neutrality. Instead,
the Caroline incident involved a general, peacetime duty of due diligence in the form
of a freestanding obligation independent of duties relating to neutrality or any other
sector-specific rule of international law. In their diplomatic resolution of the dispute,
the parties agreed: “[A]ll that can be expected from either government in these cases is
good faith, a sincere desire to preserve peace and do justice, [and] the use of all proper
means of prevention.”39
A further episode involving international law due diligence arose between the
United States and Great Britain during the American Civil War. Although Great
Britain declared its neutrality early in the conflict, British-built ships supplied to the
Confederacy sank more than 150 Union merchant ships around the world. After
protracted and heated diplomatic exchanges, the United States and Great Britain agreed
to resolve US claims from the sinkings at an ad hoc international tribunal known as
the Alabama arbitration. Among other claims, the United States alleged that Great
Britain’s failure to seize the ships amounted to a breach of due diligence.
Although the law of neutrality seemed to offer an adequate and relevant legal ground
on which to address the situation, both the parties and the tribunal resorted to the

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international law principle of due diligence to resolve the US claims. In the treaty that
formed the tribunal, the United States and Great Britain agreed:
A neutral Government is bound—
First, to use due diligence to prevent the fitting out, arming, or equipping, within
its jurisdiction, of any vessel which it has reasonable ground to believe is intended
to cruise or to carry on war against a Power with which it is at peace; and also to use
like diligence to prevent the departure from its jurisdiction of any vessel intended to
cruise or carry on war as above, such vessel having been specially adapted, in whole
or in part, within such jurisdiction, to warlike use. . . .
Thirdly, to exercise due diligence in its own ports and waters, and, as to all persons
within its jurisdiction, to prevent any violation of the foregoing obligations and
duties.40

The tribunal unanimously concluded Great Britain had violated its duty of diligence
as a neutral state and awarded the United States $15 million in damages. Importantly,
the tribunal did not attribute construction or transfer of the ships to the British
government as acts of state.41 Instead, it found that Great Britain had “failed, by
omission, to fulfil the duties” of a neutral state.42 Although frequently regarded as a
narrow ruling on the obligations of neutral states during armed conflict, the tribunal’s
decision also stands as an early articulation of states’ general international obligations
with respect to due diligence. The tribunal based its legal conclusions on the Treaty
of Washington but also cited “principles of international law.”43 In this respect, the
tribunal appears to have adopted the US position that “a reasonable ground [for
believing that an international law violation might occur] . . . ​is an element of the
question of due diligence always fairly to be considered” in judging the conduct of states
and the extent of their knowledge of harm emanating from their territory.44 Guided by
the parties’ own consensus statements of law codified in a treaty, the tribunal clearly
framed British conduct as both a breach of its due diligence duty to safeguard other
states against harm emanating from its own territory as well as a failing of neutrality.
The tribunal, at the repeated urging of the United States, laid the groundwork for due
diligence as a general and freestanding obligation of conduct in international law.
No doubt inspired by the Alabama arbitration, the Supreme Court of the United States
soon recognized the legal principle of due diligence as well. In 1887, the court upheld
a federal statute prohibiting the counterfeiting of foreign financial instruments.45
Citing de Vattel’s The Law of Nations, the court identified both a specific international
law prohibition on tolerating counterfeiters as well as a general international law duty
of due diligence to cease and redress such harm. The court held that Congress had
authority to enact the statute under its power to define the law of nations, in this case

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the duty of due diligence. The court observed: “The law of nations requires every
national government to use ‘due diligence’ to prevent a wrong being done within its
own dominion to another nation with which it is at peace, or to the people thereof.”46
A breach of due diligence with respect to counterfeiting, the court noted, “may not,
perhaps, furnish sufficient cause for war, but it would certainly give just ground of
complaint.”47
Finally, in 1937, the United States returned to international arbitration and to
due diligence to address pollution from the Canadian zinc smelter at Trail, British
Columbia, near the border with Washington State. The treaty that committed the
issue to the tribunal instructed the arbitrators to apply US law as well as “international
law and practice.”48 After confirming that pollution from the smelter caused extensive
damage to US farms and forests, the tribunal issued two decisions. The first came
in 1938, in an opinion that applied US tort law to calculate and award damages to
the United States. The first opinion also held that Canada had a duty to the United
States to cease polluting and refrain from permitting future harm. In addition, it
ordered the installation of mitigation measures and pollution detectors, but it cited no
international legal authority.
In the second decision, issued in 1941 and relying on readings from the pollution
detectors, the tribunal returned to the question of a Canadian duty of due diligence
to cease harm. The tribunal announced that “under the principles of international
law . . . ​no State has the right to use or permit the use of its territory in such a manner
as to cause injury by fumes in or to the territory of another.”49 Quoting a then
contemporary treatise on state responsibility, the tribunal also noted:
“A State owes at all times a duty to protect other states against injurious acts
by individuals from within its jurisdiction.” A great number of such general
pronouncements by leading authorities concerning the duty of a State to respect
other states and their territory have been presented to the Tribunal. These and many
others have been carefully examined. International decisions, in various matters,
from the Alabama case onward, and also earlier ones, are based on the same general
principle, and, indeed, this principle, as such, has not been questioned by Canada.
But the real difficulty often arises rather when it comes to determine what, pro
subjecta materie, is deemed to constitute an injurious act.50

Addressing the relevant threshold of harm, the tribunal held that principles of
international law identified a “serious consequence . . . ​established by clear and
convincing evidence” as the relevant injury threshold for purposes of diligence.51
The significance of early US legal and diplomatic encounters with the principle of due
diligence is clear on several points. First, on three occasions in its international legal

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relations, and in its domestic law as upheld by its highest court, the United States
relied on or confirmed a general duty of due diligence with respect to harm emanating
from a state’s territory. From the early nineteenth century through the middle of the
twentieth century, the United States steadfastly supported a general duty of territorial
due diligence. Second, in two momentous international arbitrations, breach of due
diligence claims successfully vindicated significant US national and private interests.
In both the Alabama and Trail Smelter arbitrations, international tribunals adopted US
arguments about due diligence and used these arguments to justify substantial awards
under international law.
And finally, in all three international legal episodes, the vindication of due diligence
claims contributed to a peaceful resolution of diplomatic tension between powerful
states. In each case, due diligence operated as a sort of relief valve in international
relations. The Alabama claims arose in the highly charged context of recognition by
Great Britain of a condition of belligerency between the Northern Union and the
Southern Confederacy. Paired with this diplomatic and international legal insult, the
harm resulting from British-built ships to US merchant fleets nearly brought the parties
to war. Broader political and economic considerations perhaps best explain how the
United States and Great Britain avoided war. Yet the availability of a claim for breach
of due diligence based on mere omissions to give rise to liability for an internationally
wrongful act may also have played a part in the peaceful and successful resolution of
the Alabama claims. Casting British conduct as a failure of due diligence permitted
the United States to raise the issue early, in effect freezing the facts of the dispute and
reducing the likelihood of escalatory exchanges of retorsions or even reprisals.
Similarly, although damage from the Trail smelter significantly soured US-Canadian
relations for more than a decade, the fact that the United States alleged a lapse of
diligence—an omission or oversight rather than an affirmative act that intended
harm—may explain the successful and peaceful resolution of the issue. Again, the
nature of a due diligence breach as a lapse of oversight and control rather than a
deliberate harm or even of imputed responsibility may have played a part in the
peaceful and successful resolution of the claims.
These legal and diplomatic precedents warrant consideration in present and future
US perspectives on due diligence generally. The nascent US misgivings concerning
due diligence detected by Professor Hollis suggest a change from the United States’
historical legal and diplomatic embrace of the principle. Whether the law and
conditions that informed prior US practice with respect to due diligence have
changed sufficiently to warrant this shift is relevant to the formation of US legal
policy. Similarly, whether US security interests, including those identified in the US
Defend Forward strategy, call for a change in policy toward due diligence is worthy
of examination.

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As noted previously, although legally distinct from each other, the general
international law principle of due diligence and various regime-specific expressions
of due diligence have experienced a developmental cross-pollination of sorts. Clearly
the broader principle of due diligence has inspired and informed more specific notions
of the concept. Meanwhile, doctrinal elaborations, originally developed for specific
contexts of international interaction, have found their way into academic and even
judicial descriptions of the general principle of due diligence. For instance, although
the regime-specific notion of prevention of harm presents most clearly in international
environmental law, it has featured in a number of prominent articulations of the
general obligation of due diligence. Such accounts of the due diligence principle
recite a general, as opposed to merely regime-specific, duty on the part of states to
prevent rather than just respond to and cease transboundary harm. To preserve the
traditional, unembellished principle of due diligence (i.e., without the gloss imported
from particularized applications), the United States might reject refinements such as
a duty of prevention or a threshold of harm lower than what has traditionally been
required for a breach, reserving such questions for regime-specific incarnations of the
principle.

The United States and Cyber Due Diligence
As detailed above, the United States has remained conspicuously silent on the
application of due diligence to cyberspace. Although the United States joined the
2015 UN GGE consensus document stating that “States should not knowingly allow
their territory to be used for internationally wrongful acts using ICTs,” this statement
was couched in terms of voluntary, nonbinding recommendations.52 Moreover, in its
submissions to both the 2013 and 2015 UN GGEs, the United States evidently made no
assertions as to the application of due diligence to cyber activities.
Likewise, none of the recent US government statements on cyber operations have
expressly and unequivocally embraced a doctrine of cyber due diligence. For example,
the 2018 National Cyber Strategy does not comment on due diligence.53 While
subsequent cyber strategy employed by the Department of Defense briefly recites
the due diligence principle, noting recent international consensus on a prohibition
“against allowing national territory to be used for intentionally wrongful cyber
activity,” it does not announce any conclusion on the role of cyber due diligence
in US policy.54 Nor does it indicate how breaches of due diligence by adverse actors
might justify US cyber responses under the Defend Forward strategy. In the recent
Cyberspace Solarium Commission report, the commission had the opportunity to
endorse due diligence as a means of fixing legal responsibility for harm to US interests
both at home and abroad, but it did not do so. A statement to that effect would have
been an important step in supporting the Defend Forward approach to national
security, but the commission did not take it.55

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It is unclear at this point if the lack of comment on cyber due diligence was an
intentional decision or simply reflected a lack of full consideration by the
government. Importantly, future US legal policy toward due diligence generally
may not mirror in all respects policy toward cyber due diligence. As preceding
sections have demonstrated, due diligence has lived something resembling two
lives in international law: one as a general provision of international law, and
another as a sector-specific notion tailored to the norms and demands of various
domains and conditions of international relations. While the rejection of a
general principle of due diligence and embrace of cyber due diligence would seem
inconsistent, the same would not be true if the United States supported the general
principle and rejected its application to cyber activities. As argued next, the DoD
specifically, and the United States more broadly, ought to accept a tailored doctrine
of cyber due diligence and advocate for its adoption throughout the international
community.

Cyber Due Diligence and Defending Forward
In a recent speech, the Honorable Paul C. Ney, general counsel of the DoD, described
the Defend Forward strategy. He explained:
A key element of the US military’s strategy in the face of these cyber-threats
is to “defend forward.” Implementing this element of the strategy begins with
continuously engaging and contesting adversaries and causing them uncertainty
wherever they maneuver—which we refer to as “persistent engagement.” Persistent
engagement recognizes that cyberspace’s structural feature of interconnectedness
and its core condition of constant contact creates a strategic necessity to operate
continuously in cyberspace. As General [Paul M.] Nakasone has said, “If we find
ourselves defending inside our own networks, we have lost the initiative and the
advantage.” In short, the strategy envisions that our military cyber forces will be
conducting operations in cyberspace to disrupt and defeat malicious cyber activity
that is harmful to US national interests.56

The United States has thus concluded that operating outside of domestic cyber
infrastructure is essential to effectively respond to significant cyber harm and to
preserve national security. The strategy clearly indicates that the United States will
maintain a presence and conduct operations in cyber networks outside its own
borders, on the sovereign territory of other states. Although neither the strategy itself
nor Ney’s remarks expressly couples Defend Forward with specific international legal
justifications, it is clear persistent engagement on foreign networks requires such legal
work. Due diligence, particularly as expressed in past US diplomatic and legal practice,
presents an enticing legal basis to support operations that respond to harm emanating
from foreign networks and cyber infrastructure.

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Endorsing cyber due diligence would provide a number of direct and immediate
benefits to the Defend Forward approach. First, legal and technical attribution have
always been vexing in the cyber context. The internet facilitates anonymity, at least
in the short term, and allows states and nonstate actors to operate without fear of
immediate accountability. Further, the legal regime of state responsibility sets a high
bar for attributing the actions of nonstate proxy actors to states themselves.57 In fact, it
is likely that the difficulties associated with attribution in cyberspace motivated the US
Defend Forward strategy. We have previously addressed this subject and argued:
[A] primary rule of conduct requiring diligent management of territorial cyber
infrastructure could give rise to responsibility on the part of nondiligent states as
proxies for unidentified or unreachable malicious actors. Legal recognition of such
breaches of diligence permits State victims of cyber harm to take action to induce
compliance and terminate harm without necessarily tracing attribution to the
original, difficult-to-identify source.58

In other words, reaffirming and clarifying the duty of due diligence would permit the
United States to hold territorial states responsible for transboundary cyber harms and
react using self-help measures, regardless of whether the United States could accurately
identify the actual source of the harm—whether the government of the territorial
state itself, a state proxy, or a nonconnected entity or individual. Such an approach,
appropriately applied, would relieve the United States, and other states, of significant
forensic difficulties and dramatically strengthen accountability across the international
community.
Additionally, endorsing due diligence would support the GGE process of clarifying
cyber obligations under international law. Due diligence did receive a mention,
though aspirational, in the GGE’s 2015 consensus document. The participating
states, including cyber superpowers, offered “recommendations for consideration by
states for voluntary, non-binding norms, rules or principles of responsible behaviour
of states aimed at promoting an open, secure, stable, accessible and peaceful ICT
environment.”59 By reaffirming the principle of due diligence and clarifying its
approach in cyberspace, the United States would not only set a marker for the
international community during norm development. It would also provide notice to
allies and adversaries alike of US intentions as they formulate their own approaches to
this question, including their reactions to the US Defend Forward policy.
These considerations provide ample reason for the United States to embrace cyber
due diligence as a legal justification for its Defend Forward approach to national
security. However, as the United States crafts its international legal policy toward due
diligence, four doctrinal aspects deserve special consideration. First, some recitations
of cyber due diligence have included an obligation to proactively monitor and prevent

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 14

transboundary harmful activities. This is not the prevailing approach and should
not be the approach the United States adopts. Rather, the United States should
make clear that neither the general principle of due diligence nor any obligation of
cyber-specific due diligence includes a duty to monitor and prevent. Second, any
endorsement of cyber due diligence should require a threshold of harm amounting
to “serious adverse consequences” before liability attaches. Third, acceptance of
cyber due diligence should be understood only to require feasible measures on
the part of territorial states. Finally, the United States should bear in mind and
warn of the potential escalatory nature of cyber due diligence—particularly with
respect to the potential use of countermeasures—and take affirmative steps to build
safeguards against such danger.
In addition to the basic due diligence duty that states quell harm emanating from
their territories, some sources have referred to an ex ante duty to prevent such harm
from starting in the first place. Under a sector-specific conception of due diligence,
some advocates of cyber due diligence have argued that this means states have a
duty to monitor and prevent transboundary cyber harms. The ICJ, for instance, has
repeatedly endorsed a duty to exercise due diligence to prevent transboundary harm
in the international environmental law context.60 By contrast, the Tallinn Manual 2.0
drafters did not identify a duty to monitor and prevent transboundary cyber harms.
They agreed that the duty of due diligence extends to cyberspace, but indicated
that this duty “is not to be interpreted as including a requirement of monitoring
or taking other steps designed to alert authorities to misuse of cyber infrastructure
located on the State’s territory.”61 Indeed, the drafters concluded that “it would be
unreasonable to assert that an obligation of prevention exists in the cyber context[;]
[s]uch a requirement would impose an undue burden on States, one for which there
is no current basis in either the extant law or current State practice.”62 They noted
inadequate evidence that states had expressed either in statements or practice a sense
of legal obligation to take preventive measures. Nor had states legally condemned
failures to take preventive measures.
In addition to their practical and precedential reasons for rejecting a duty of
prevention, states have not adopted this duty out of a concern that “obligations
of States under international human rights law could run counter to such a duty,
depending on how it was fulfilled.”63 For example, an authoritarian state might
monitor electronic communications, allowing the repression or censorship of
unfriendly or politically nonsupportive communications, under the guise of the
duty to prevent transboundary harm. The United States, in adopting a duty of
cyber due diligence, should be clear that this duty does not justify a country’s
monitoring all cyber communications within its territory, nor does it provide
any excuse for potential human rights (or more likely domestic constitutional)
violations.

Eric Talbot Jensen and Sean Watts  •  Due Diligence and the US Defend Forward Cyber Strategy

 15

In the same regard, the United States might dampen the obligation of cyber due
diligence by indicating that not all cyber harm triggers it. To this end, the United
States should advocate for a relatively high threshold of harm as a prerequisite to a
breach of due diligence. The United States has already expressed support for this view
in multiple contexts, including in the 2018 National Cyber Strategy, which lists one
of the DoD’s cyberspace objectives as “[d]efending U.S. critical infrastructure from
malicious cyber activity that alone, or as part of a campaign, could cause a significant
cyber incident.”64 The document then defines a “significant cyber incident” as “an
event occurring on or conducted through a computer network that is . . . ​likely to
result in demonstrable harm to the national security interests, foreign relations, or
economy of the United States or to the public confidence, civil liberties, or public
health and safety of the American people.”65
The Tallinn Manual 2.0 drafters agreed that a high threshold of harm was a prerequisite
for the onset of the due diligence obligation in cyber operations. They further noted:
The precise threshold of harm at which the due diligence principle applies is
unsettled in international law. All of the Experts agreed that the due diligence
requirement arises when the situation involves a cyber operation that results in
“serious adverse consequences”, [sic] although they could identify no bright line
threshold for the identification of such consequences.66

By simultaneously embracing a duty of cyber due diligence and making clear that
the duty is subject to a threshold of harm such as “serious adverse consequences,”
the United States can help ensure that the duty is appropriately circumscribed while
preserving operational prerogative with respect to the kinds of minimally intrusive
operations the Defend Forward strategy envisions.
Some detractors of the due diligence obligation argue that the standard of conduct
is too high and will impose unachievable demands on states. A robust conception of
due diligence, such as that emerging in the context of international environmental
law, might indeed implicate this concern. However, consistent with international
precedent (including the US experience), the Tallinn Manual 2.0 requires that a state
have actual or constructive knowledge of transboundary harm before a due diligence
obligation attaches.67 With respect to Defend Forward operations, the United States
should not be required to have conclusive or even direct evidence that a territorial
state had knowledge of the harm coming from its territory in order for a breach of due
diligence assertion to be applicable on the part of that state. Circumstantial or indirect
evidence should suffice. The requirement of knowledge, combined with the lack of
an obligation to monitor or prevent harm ex ante, removes some of the affirmative
obligations sometimes associated with due diligence. These limits on the due diligence
principle would also place states in a position of potentially cooperative remediation,

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particularly in the face of nonstate cyber activities. If the United States adopts cyber
due diligence, it should do so with the same caveats.
Once knowledge is established, due diligence requires a state to take actions to cease
or put a stop to the transboundary harm. This might also seem like a potentially
arduous standard for states to achieve, even for the United States, with its immense
technological resources and capabilities. However, again in accord with the Tallinn
Manual 2.0, the standard is not one of strict liability. States are only required to take
feasible actions necessary to prevent further harm.68 In this context, feasibility is
understood to mean that which is practicable or practically possible. In other words,
a state with knowledge of harm arising out of its territory must take feasible actions
to try to prevent further harm, but it is not required to take all possible actions. If the
United States embraces the principle of cyber due diligence, it should likewise clarify
for both the international community and its allies and partners that feasibility is the
appropriate standard for compliance.
Finally, the United States should draw particular attention to the potentially
escalatory nature of responses to failures to exercise cyber due diligence and take
affirmative steps to guard against such danger. If an obligation of cyber due diligence
is adopted as an international norm, failure to honor the obligation would amount
to an internationally wrongful act, allowing the victim state to respond with
countermeasures. Cyber countermeasures are adapting to modern state interaction,
and continue to provide a very effective tool to encourage violating states to move
back into compliance with international law.69 However, aggressive countermeasures
also risk escalation and instability.70 Because countermeasures are adapting alongside
cyber capabilities, the United States should engage with like-minded members of the
international community on appropriately limiting countermeasures in response to
cyber offenses as part of its Defend Forward strategy.
Embracing the obligation of cyber due diligence and taking the approach advocated
here is not without significant potential drawbacks for the United States. For example,
the United States is among the leading countries of origin for transnational cyber
hacks.71 The United States’ extensive computer infrastructure is also a desirable target
for establishing botnets controlled from outside the United States. McAfee recently
reported that the United States was host to more botnets than Russia and China
combined.72
Both of these facts have significant implications for the United States’ adoption of due
diligence obligations. Because so much transboundary harm originates from within
the United States, victim states would be able to attribute those actions to the United
States and take appropriate actions based on that attribution. Even given the “serious
adverse consequences” and “feasibility” limitations discussed above, the sheer volume

Eric Talbot Jensen and Sean Watts  •  Due Diligence and the US Defend Forward Cyber Strategy

 17

of transboundary harm emanating from the United States would impose a significant
remediation requirement on the government.
Despite these potential issues, we still recommend that the United States endorse due
diligence in the manner described above. It is our view that the benefits from adopting
cyber due diligence, in an appropriately limited form, would result in greater gains
than drawbacks for the United States. Adoption of cyber due diligence obligations
would provide meaningful benefits, including but not limited to adding clarity for
state practice, accelerated norm development, and a partial resolution to the issue of
cyber attribution.

Conclusion
The Defend Forward strategy clearly communicates an evolution in the US approach to
emerging threats in cyberspace. No longer content to merely fortify domestic networks
and infrastructure, the United States envisions a proactive and externally focused
response regime. US reactions to harm emanating from foreign territory will likely
include persistent, nonconsensual operations on foreign government and private cyber
infrastructure. Perhaps just as important as the technical effects of these responses
is the fact that the United States has put the world on notice regarding its intent to
undertake them. The strategy is not just an administrative instruction to US agencies.
It is a deliberate strategic message to US competitors and adversaries in cyberspace.
Threats in cyberspace and US reactions to those threats call for equally clear and
effective legal messaging. To be credible to both adversaries and allies, the US cyber
strategy requires sound, unambiguous legal justifications. Among other international
law provisions relevant to cyberspace, due diligence offers promising legal support for
Defend Forward operations. Confronted with harm emanating from foreign territory,
states have resorted to due diligence for both legal redress and to justify self-help
responses. In many cases, the nonconsensual and intrusive cyber operations that likely
form the core of the Defend Forward strategy could be justified as measures of self-help
undertaken in response to breaches of due diligence.
However, there is increasing evidence that the US position on due diligence is at least
circumspect and at worst cynical. The United States should carefully evaluate these
views and their motives. There is extraordinarily strong support among a variety of
accepted sources of international law for due diligence as a freestanding obligation
of state conduct. Extensive and consistent US foreign relations practice played a
critical role in the formation of this norm, and throughout its history, the United
States has enjoyed peaceful and profitable diplomatic outcomes by invoking the
due diligence doctrine. In light of this experience and the promising legal utility of
cyber due diligence to the Defend Forward strategy, the United States should endorse

Hoover Institution  •  Stanford University

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due diligence as a general obligation of international law. Further, it should clearly
express the legal duties as well as the doctrinal limits associated with due diligence in
cyberspace. A clearly defined US legal policy toward due diligence, incorporating the
provisions outlined in this chapter, will both support the vital US security interests
identified in its cyber strategy and reassert influence on a critical component of the
regulation of modern international relations.

NOTES
1 ​US Dep’t of Defense, Summary: Department of Defense Cyber Strategy 2018, at 1 (2018) [hereinafter
2018 Strategy Summary]. Only a summary of the strategy is available publicly. Presumably, the full strategy
is circulated in government as a classified document.
2 ​Id. at 2.
3 ​Id. at 1.
4 ​Commentators also refer to a “no harm principle” in this respect. See Timo Koivurova, Due Diligence, in
Max Planck Encyclopedia of Public International Law ¶¶ 2, 11 (Rüdiger Wolfrum ed. 2010).
5 ​See Ashley Deeks, “Defend Forward and Cyber Countermeasures,” Hoover Working Group on National
Security, Technology, and Law, Aegis Series Paper No. 2004 (examining countermeasures and associated
doctrinal limits as a legal facet of the US Defend Forward strategy), August 4, 2020, https://­www​.­lawfareblog​
.­com​/­defend​-­forward​-­and​-­cyber​-­countermeasures.
6 ​See Eric Talbot Jensen and Sean Watts, A Cyber Duty of Due Diligence: Gentle Civilizer or Crude
Destabilizer?, 95 Tex. L. Rev. 1555, 1557–58 (2017).
7 ​See Duncan B. Hollis, International Law and State Cyber Operations: Improving Transparency:
Fourth Report 24–26 (2020).
8 ​See e.g., Greg Lynham, The Sic Utere Principle as Customary International Law: A Case of Wishful Thinking, 2
James Cook U. L. Rev. 172, 184–86 (1995).
9 ​Jutta Brunnée, Sic utere tuo ut alienum non laedas, in Max Planck Encyclopedia of Public International
Law (Rüdiger Wolfrum ed. 2010).
10 ​
Robert Phillimore, 1 Commentaries upon International Law xxi (2d ed. 1871).
11 ​
L assa Oppenheim, 1 International Law: A Treatise 203, 211 (1905).
12 ​
Hersch Lauterpacht, Private Law Sources and Analogies of International Law 217 (1927) (internal
citation omitted).
13 ​In the 1925 British Claims in the Spanish Zone of Morocco arbitration, Max Huber ruled that a State that
“failed to exercise due diligence in preventing or punishing the unlawful actions of armed groups could be
held responsible for such failure.” British Claims in the Spanish Zone of Morocco (Gr. Brit. v. Spain), 2 R.I.A.A.
617, 642–46 (1925).
14 ​Corfu Channel (U.K. v. Alb.), Merits, 1949 I.C.J. Rep. 4, 10 (Apr. 9).
15 ​
Id. at 22.
16 ​
Cf. Jörg Schildknecht, Belligerent Rights and Obligations in International Straits, in Operational Law
in International Straits and Current Maritime Security Challenges 78 (Jörg Schildknecht et al., eds.,
2018).

Eric Talbot Jensen and Sean Watts  •  Due Diligence and the US Defend Forward Cyber Strategy

 19

17 ​Convention Relative to the Laying of Automatic Submarine Contact Mines (Hague No. VIII), art. 3–4,
Oct. 18, 1907, 36 Stat. 2332.
18 ​Corfu Channel, 1949 I.C.J. Rep. at 78, 84 (dissenting opinion of Azevedo, J.); see also Memorial Submitted
of United Kingdom, Corfu Channel, 1949 I.C.J. Pleadings at 19, 36–38 (Sept. 30).
19 ​Pulp Mills on the River Uruguay (Arg. v. Uru.), Judgment, 2010 I.C.J. Rep. 14, ¶ 101, 197 (Apr. 20).
Ultimately the Court did not find Uruguay had breached its duty of diligence as a matter of fact. Id. at ¶ 265.
20 ​Id. at ¶ 101 (quoting Corfu Channel, 1949 I.C.J. Rep. at 22).
21 ​Certain Activities Carried Out by Nicaragua in the Border Area (Costa Rica v. Nicar.), Judgment, 2015
I.C.J. Rep. 665 (Dec. 16).
22 ​ILA, ILA Study Group on Due Diligence in International Law: First Report 1 (2014).
23 ​ILA, ILA Study Group on Due Diligence in International Law: Second Report 47 (2016).
24 ​
Id. at 6.
25 ​Anders Henriksen, The End of the Road for the UN GGE Process: The Future Regulation of Cyberspace, J.
Cyber sec., 1–2 (2019) (quoting Martha Finnemore & Kathryn Sikkink, International Norm Dynamics and
Political Change, 52 Int Org. 887, 896 [1998]).
26 ​Group of Governmental Experts on Developments in the Field of Information and Telecommunications
in the Context of International Security, ¶ 19, UN Doc. A/68/98 (June 24, 2013).
27 ​Group of Governmental Experts on Developments in the Field of Information and Telecommunications
in the Context of International Security, ¶ 13, UN Doc. A/70/174 (July 22, 2015) [hereinafter 2015 UN GGE
Report].
28 ​
Id.
29 ​European Council and Council of the EU, “Declaration by the High Representative Josep Borrell,
on Behalf of the European Union, On Malicious Cyber Activities Exploiting the Coronavirus Pandemic”
press release, August 12, 2020, https://­w ww​.­consilium​.­europa​.­eu​/­en​/­press​/­press​-­releases​/­2020​/­0 4​/­30​
/­declaration​-­by​-­the​-­high​-­representative​-­josep​-­borrell​-­on​-­behalf​-­of​-­the​-­european​-­union​-­on​-­malicious​
-­cyber​-­activities​-­exploiting​-­the​-­coronavirus​-­pandemic​/­.
30 ​
Id.
31 ​
Hollis, supra note 7, at 24–26.
32 ​
Id. at 25.
33 ​Ministry of the Armies, International Law Applicable to Operations in Cyberspace 10 (2019) (Fr.);
Letter from the Minister of Foreign Affairs to the President of the House of Representatives, Letter to the
Parliament on the International Legal Order in Cyberspace, Appendix at 4 (Jul. 5, 2019) (Neth.); Kersti
Kaljulaid, President, The Republic of Estonia, Speech at the Opening of the International Conference on
Cyber Conflict (CyCon) 2019 (May 29, 2019).
34 ​
Tallinn Manual 2.0 on the International Law Applicable to Cyber Operations 31 (Rule 6) cmt. 4
(Michael N. Schmitt ed., 2d ed. 2017) [hereinafter Tallinn Manual 2.0]. Both authors were members of the
international group of experts who drafted the Tallinn Manual. The General Editor of the Tallinn Manual has
also written separately on due diligence in cyberspace. See Michael N. Schmitt, In Defense of Due Diligence
in Cyberspace, 125 Yale L.J.F. 68 (2015).
35 ​
Tallinn Manual 2.0, supra note 34, at 30 (Rule 6).
36 ​
Hollis, supra note 7, at 20.

Hoover Institution  •  Stanford University

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37 ​
Id. at 25–26.
38 ​See John Bassett Moore, 7 A Digest of International Law 919–20 (1906) (describing the incident and
the US Secretary of State’s instructions to district attorneys in Northern states to abstain from involvement
in the rebellion); see also Maurice G. Baxter, One and Inseparable: Daniel Webster and the Union 321
(1984) (describing President Van Buren’s strict policy of neutrality in the rebellion).
39 ​Elizabeth Chadwick, The British View of Neutrality in 1872, in Notions of Neutralities 87, 93 (Pascal
Lottaz & Herbert R. Reginbogin eds., 2019) (emphasis added). In response to the incident, the United States
amended its domestic neutrality laws to better authorize federal interventions and seizures. Id. at 93 (citing
Act of March 10, 1838, Ch. 31, 5 Stat. 212); see also Bassett Moore, supra note 40, at 920 (describing events,
including a request from President Van Buren, leading to amendment of US neutrality laws).
40 ​Treaty of Washington, US-U.K., art. VI, May 8, 1871, 17 Stat. 863, T.S. No. 133.
41 ​
See generally Ala. Claims Arbitration (US v. Gr. Brit.) 29 R.I.A.A. 125 (1872).
42 ​
Id. at 131.
43 ​
Id. at 129, 132.
44 ​William Evarts, Counsel of the United States, Argument Addressed to the Tribunal of Arbitration at Geneva,
on the 5th and 6th August 1872, in Reply to the Special Argument of the Counsel of Her Britannic Majesty,
Supplement to the London Gazette, Oct. 4, 1872, at 4643.
45 ​United States v. Arjona, 120 US 479 (1887).
46 ​Id. at 484.
47 ​
Id. at 487.
48 ​Convention for the Final Settlement of the Difficulties Arising through Complaints of Damage Done in
the State of Washington by Fumes Discharged from: The Smelter of the Consolidated Mining and Smelting
Company, Trail, British Columbia, US-Can., art. IV, Apr. 15, 1935, 162 L.N.T.S 73.
49 ​Trail Smelter Arbitration (US v. Can.), 3 R.I.A.A. 1905, 1965 (1941).
50 ​Id. at 1963 (quoting Clyde Eagleton, Responsibility of states in International Law 80 [1928]).
51 ​
Id. at 1965.
52 ​2015 UN GGE Report, supra note 29, at ¶ 13(c).
53 ​See Office of the President, National Cyber Strategy of the United States of America (2018).
54 ​2018 Strategy Summary, supra note 1, at 5.
55 ​
US Cyber Solarium Commission, Final Report (2020).
56 ​Hon. Paul C. Ney Jr., Gen. Counsel, Dep’t of Defense, DOD General Counsel Remarks at the US Cyber
Command Legal Conference (Mar. 2, 2020) (some internal quotations omitted).
57 ​Int’l L. Comm’n, Rep. of the Int’l Law Comm’n on the Work of Its Fifty-Third Session, Draft Articles on
Responsibility of states for Internationally Wrongful Acts, art. 8, UN Doc. A/56/10, at 47 (2001).
58 ​Jensen and Watts, supra note 6, at 1558.
59 ​2015 UN GGE Report, supra note 27, at ¶ 13.
60 ​
See, e.g., Pulp Mills on the River Uruguay (Arg. v. Uru.), Judgment, 2010 I.C.J. Rep. 14, ¶ 101 (Apr. 20).
61 ​The Tallinn Manual 2.0 states that: “A State must exercise due diligence in not allowing its territory, or
territory or cyber infrastructure under its governmental control, to be used for cyber operations that affect

Eric Talbot Jensen and Sean Watts  •  Due Diligence and the US Defend Forward Cyber Strategy

 21

the rights of, and produce serious adverse consequences for, other states.” Tallinn Manual 2.0, supra note
34, at 30 (Rule 6); Id. at 42 (Rule 6) cmt. 42.
62 ​
Id. at 45 (Rule 7) cmt. 8.
63 ​
Id. at 45 (Rule 7) cmt. 8.
64 ​2018 Strategy Summary, supra note 1, at 3 (emphasis added).
65 ​Id. at 3, n. 3 (internal citation omitted).
66 ​
Tallinn Manual 2.0, supra note 34, at 36–37 (Rule 6) cmt. 25.
67 ​Id. at 40 (Rule 6) cmts. 37–39.
68 ​
Id. at 43 (Rule 7).
69 ​See generally Deeks, supra note 5.
70 ​Jensen and Watts, supra note 6, at 1569–74.
71 ​“Top 10 Countries with Most Hackers in the World,” Cyware Social, September 7, 2016, https://­cyware​
.­com​/­news​/­top​-­10​- ­countries​-­with​-­most​-­hackers​-­in​-­the​-­world​- ­42e1c94e; “The Top 5 Countries Where Cyber
Attacks Originate From,” ARK Systems, March 16, 2017, https://­w ww​.­arksysinc​.­com​/­blog​/­top​-­5 ​- ­countries​
- ­cyber​-­attacks​- ­originate​/­.
72 ​Emil Protalinski, “McAfee: US Hosts More Botnet Servers than Any Other Country, More than Russia and
China Combined,” TNW, January 24, 2013, https://­thenextweb​.­com​/­insider​/­2013​/­01​/­24​/­mcafee​-­us​-­hosts​
-­more​-­botnet​-­servers​-­than​-­any​-­other​-­country​-­more​-­than​-­russia​-­and​-­china​-­combined​/­.

Hoover Institution  •  Stanford University

 23

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7 ​6 ​5 ​4 ​3 ​2 ​1

The preferred citation for this publication is Eric Talbot Jensen and Sean Watts, Due Diligence and the US Defend
Forward Cyber Strategy, Hoover Working Group on National Security, Technology, and Law, Aegis Series Paper No. 2006
(October 15, 2020), available at https://­w ww​.­lawfareblog​.­com​/­due ​- ­diligence ​-­and​-­us​- ­defend​-­forward​- ­c yber​-­strategy.

Hoover Institution  •  Stanford University

 About the Authors

Working Group on National Security, Technology,
and Law
The Working Group on National Security, Technology, and
Law brings together national and international specialists
with broad interdisciplinary expertise to analyze how
technology affects national security and national security
law and how governments can use that technology to defend
themselves, consistent with constitutional values and the rule
of law.

ERIC TALBOT JENSEN
Eric Talbot Jensen is the Robert
W. Barker Professor of Law at
Brigham Young University Law
School. Previously, he taught at
Fordham University and served in
the US Army for more than twenty
years as a cavalry officer and a judge
advocate. He recently returned from
a year as the special counsel to the
Department of Defense general
counsel.

The group focuses on a broad range of interests, from
surveillance to counterterrorism to the dramatic
impact that rapid technological change—digitalization,
computerization, miniaturization, and automaticity—are
having on national security and national security law. Topics
include cybersecurity, the rise of drones and autonomous
weapons systems, and the need for—and dangers of—state
surveillance. The group’s output will also be published on
the Lawfare blog, which covers the merits of the underlying
legal and policy debates of actions taken or contemplated
to protect the nation and the nation’s laws and legal
institutions.
Jack Goldsmith is the chair of the National Security,
Technology, and Law Working Group.
For more information about this Hoover Institution Working
Group, visit us online at http://­w ww​.­hoover​.­org​/­research​-­teams​
/­national​-­security​-­technology​-­law​-­working​-­g roup.

SEAN WATTS
Sean Watts is a professor in the
Department of Law, US Military
Academy at West Point, where he
codirects the Lieber Institute for the
Law of Land Warfare. He is a senior
fellow with the NATO Cooperative
Cyber Defence Center of Excellence
in Tallinn, Estonia. He served in the
US Army as a military lawyer and
an armor officer.

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