According to a recent report by the Electronic Frontier Foundation (EFF), data brokers harvest location data from mobile apps and then sell it to government agencies including state and local law enforcement, ICE, the FBI, the Department of Homeland Security and the Department of Defense.
Many of the apps on a mobile device track and record location data. These include navigation apps, social media apps, and weather apps, among many others. According to EFF, once a user gives an app permission to access location data, it typically has "free rein" to share it with just about anybody. Government agencies take advantage of these loose standards to purchase troves of location data relating to millions of individuals from data brokers.
"Once in government hands, the data is used by the military to spy on people overseas, by ICE to monitor people in and around the U.S., and by criminal investigators like the FBI and Secret Service."