Adtech uses the basic lifeblood of digital commerce—the trail of data that comes off nearly all mobile phones—to deliver valuable intelligence information. Edward Snowden’s 2013 leaks showed that, for a time, spy agencies could get data from digital advertisers by tapping fiber-optic cables or internet choke points. But in the post-Snowden world, more and more traffic like that was being encrypted; no longer could the National Security Agency pull data from advertisers by eavesdropping. So it was a revelation—especially given the public outcry over Snowden’s leaks—that agencies could just buy some of the data they needed straight from commercial entities. One technology consultant who works on projects for the US government explained it this way to me: “The advertising technology ecosystem is the largest information-gathering enterprise ever conceived by man. And it wasn’t built by the government.”