April 4 (UPI) -- The Department of Homeland Security said it has confirmed the existence of mobile snooping devices around Washington, D.C. -- by either foreign actors or criminals.
The devices -- known as stingrays, cell-site simulators or Mobile Subscriber Identity-catchers -- act as fake cellphone towers and can intercept messages and conversations as mobile phones connect to the towers.
"The National Protection and Programs Directorate has observed anomalous activity in the National Capital Region that appears to be consistent with International Mobile Subscriber Identity catchers," the letter to Wyden, dated March 26, said.
The department has not yet determined the devices' origin but said they could be the result of foreign governments' activities.
U.S. officials did not elaborate on how many devices were discovered or where they were found.
The letter said the Federal Communications Commission has authorized use of snooping devices since 2011, but only to local, state and federal law enforcement agencies.
Christopher Krebs, a DHS official and top leader of the NPPD, said 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."
Krebs said in the letter that the threat of snooping devices was recognized and addressed in a DHS report in April 2017.