Office of the Under Secretary Notional Protection and Programs Directorate U.S. Department of Homeland Security Washington, DC 20528 g?nrk?, Homeland kg Security 4ND s? ?h a0 March 26, 2018 The Honorable Ron Wyden United States Senate Washington, DC 20510 Dear Senator Wyden: Thank you for your November 17, 2017 letter. International Mobile Subscriber Identity (IMSI) catchers enable the surveillance of cellular communications and devices. Since 201 l, the Federal Communications Commission (FCC) has granted authorizations for such equipment. According to the FCC, the equipment authorizations for each of these devices has limited their marketing and sale to federal, state, local public safety and law enforcement of?cials only, and required state and local law enforcement agencies to advance coordinate with the Federal Bureau of Investigation on the acquisition and use of the equipment. Use of IMSI catchers by malicious actors to track and monitor cellular users is unlawful and threatens the security of communications, resulting in safety, economic, and privacy risks. The National Protection and Programs Directorate WPPD) continues to work with the FCC, the Communications Information Sharing and Analysis Center, and other governmental and non? governmental organizations to assess the national security and other risks associated with these vulnerabilities as well as methods to mitigate these risks. IMSI catcher threats were addressed in the Study on Mobile Device Security published by the Department of Homeland Security during April 2017. The report recommended areas for additional research or partnerships. Overall, NPPD believes the malicious use of IMSI catchers is a real and growing risk. Thank you again for your letter. Responses to your speci?c questions are enclosed. Sincerely, Christo er C. Krebs Senior Of?cial Performing the Duties of the Under Secretary Enclosure