Ars Technica reports that in a March 26 letter to Oregon Sen. Ron Wyden, the Department of Homeland Security acknowledged for the first time ever that the use of unauthorized cell-site simulators in Washington D.C. The devices, known commonly as Stingrays because of one brand name or International Mobile Subscriber Identity-catchers, trick mobile devices into believing they are cell towers. Once locked in, the devices can steal data, pinpoint user locations, and/or plant malware. "Overall, [The Department of Homeland Security's National Protection and Programs Directorate] believes the malicious use of IMSI catchers is a real and growing risk," wrote Christopher Krebs, DHS' acting undersecretary in the letter to Wyden. Police around the country use the Stingrays, but they usually do not admit to it. "In 2015, various federal law enforcement agencies, including the FBI, said that, in most circumstances, they will require a warrant when they use a stingray. Some states also impose similar requirements," the Ars Technica report says. The DHS letter says it is aware of non-police use of the devices in other cities, although it also says it does not know how to detect their usage. Activists have complained about police usage of the devices because they don't pinpoint targets, but sweep up many cell phones where they are located.