A federal study found signs that surveillance devices for intercepting cellphone calls and texts were operating near the White House and other sensitive locations in the Washington area last year. From a report: A Department of Homeland Security program discovered evidence of the surveillance devices, called IMSI catchers, as part of federal testing last year, according to a letter from DHS to Sen. Ron Wyden (D-Ore.) on May 22. The letter didn't specify what entity operated the devices and left open the possibility that there could be alternative explanations for the suspicious cellular signals collected by the federal testing program last year. The discovery bolsters years of independent research suggesting that foreign intelligence agencies use sophisticated interception technology to spy on officials working within the hub of federal power in the nation's capital. Experts in surveillance technology say that IMSI catchers -- sometimes known by one popular brand name, StingRay -- are a standard part of the tool kit for many foreign intelligence services, including for such geopolitical rivals as Russia and China.