Earlier this month, it was revealed that the Department of Justice uses small devices attached to Cessna airplanes to collect data from Americans' mobile phones. Now, the American Civil Liberties Union (ACLU) is requesting more information on the surveillance program by filing a Freedom of Information Act request (PDF).

The two-foot-square devices, called “dirtboxes,” were said to operate similarly to the cell towers used by major communications firms, and were capable of capturing location data from tens of thousands of mobile phones in a single flight, the Wall Street Journal found. The report also revealed that the program was run by the U.S. Marshals Service agency (within DOJ), and began operating fully around 2007.

The digital rights group requested information on DOJ's policies for using cell simulators deployed on aircrafts, including when a warrant must be obtained.