US Homeland Security uncover electronic surveillance devices in use in Washington DC

IMSI catchers in the US capital appear to be ordinary cell towers, but are intercepting phone calls

The Department of Homeland Security has uncovered electronic surveillance devices in the US capital after it found International Mobile Subscriber Identity (IMSI) catchers in Washington DC.

The devices apparently appear to be cell towers but, in actual fact, intercept signals on mobile phones to listen in on messages and calls.

While it's already known that the FBI uses a similar surveillance tech in its "Stingray" program - which consists of suitcase-sized devices that can sweep-up data from entire neighbourhoods - this is the first time the US government has spoken of what is presumed to be foreign agents using it.

The DHS sent a letter on 26 March to Oregon Democrat Senator Ron Wyden, as reported by the Associated Press.

The malicious use of IMSI catchers is a real and growing risk

A senior DHS official, Christopher Krebs, said in the letter that the agency had "observed anomalous activity" that was "consistent" with IMSI catchers in Washington DC, but it wasn't sure who was behind the spying. The DHS also noted it needed more funding to better detect these devices.

"NPPD [National Protection and Programs Directorate] agrees that the use of IMSI catchers by foreign governments may threaten US national and economic security," the letter said, responding to Senator Wyden, who earlier requested answers from the agency in a letter dated November asking about the presence of IMSI catchers in the US capital.

Wyden asked the Federal Communications Commission (FCC) in the past to investigate Stingray technology, since the agency regulates the airwaves across the US.

"Despite repeated warnings and clear evidence that our phone networks are being exploited by foreign governments and hackers, FCC chairman Pai has refused to hold the industry accountable and instead is prioritising the interests of his wireless carrier friends over the security of Americans' communications," Wyden said in a statement.

Krebs' letter to Wyden concludes: "Overall, the NPPD believes the malicious use of IMSI catchers is a real and growing risk."