News broke this week of the U.S. Marshals Service program that's been ongoing since 2007 to gather information from Americans' cellphones. It uses small fixed-wing Cessnas equipped with 'dirtboxes' that imitate cell towers to get identifying information from citizens. According to those familiar with the program, these planes make regular flights and can scoop up data from tens of thousands of phones in densely populated areas. The program is meant to locate individuals under investigation and fugitives, but it collects information from all cellphones.
Americans’ Cellphones Targeted in Secret U.S. Spy Program (WSJ)