The Wall Street Journal reports on a surveillance program gathering the data of thousands of mobile phones:
WASHINGTON—The Justice Department is scooping up data from thousands of mobile phones through devices deployed on airplanes that mimic cellphone towers, a high-tech hunt for criminal suspects that is snagging a large number of innocent Americans, according to people familiar with the operations. […]
Planes are equipped with devices—some known as “dirtboxes” to law-enforcement officials because of the initials of the Boeing Co. unit that produces them—which mimic cell towers of large telecommunications firms and trick cellphones into reporting their unique registration information.
The technology in the two-foot-square device enables investigators to scoop data from tens of thousands of cellphones in a single flight, collecting their identifying information and general location, these people said. […]
Cellphones are programmed to connect automatically to the strongest cell tower signal. The device being used by the U.S. Marshals Service identifies itself as having the closest, strongest signal, even though it doesn’t, and forces all the phones that can detect its signal to send in their unique registration information.
Even having encryption on a phone, such as the kind included on Apple Inc. ’s iPhone 6, doesn’t prevent this process.
The technology is aimed at locating cellphones linked to individuals under investigation by the government, including fugitives and drug dealers, but it collects information on cellphones belonging to people who aren’t criminal suspects, these people said. They said the device determines which phones belong to suspects and “lets go” of the non-suspect phones.
Read the full article for many more details and a graphic explaining the technology.