The largest such file known to have been examined by journalists, it reveals more than 50 billion location pings from the phones of more than 12 million Americans across several major cities.

By analyzing these pings, our journalists were able to track the movements of President Trump’s Secret Service guards and of senior Pentagon officials. They could follow protesters to their homes and stalk high-school students across Los Angeles. In most cases, it was child’s play for them to connect a supposedly anonymous data trail to a name and an address — to a real live human being.