In its 10 years of operation, Grindr had amassed millions of users and become a central cog in gay culture around the globe.

But to Yeagley, Grindr was something else: one of the tens of thousands of carelessly designed mobile phone apps that leaked massive amounts of data into the opaque world of online advertisers. That data, Yeagley knew, was easily accessible by anyone with a little technical know-how. So Yeagley—a technology consultant then in his late forties who had worked in and around government projects nearly his entire career—made a PowerPoint presentation and went out to demonstrate precisely how that data was a serious national security risk.

As he would explain in a succession of bland government conference rooms, Yeagley was able to access the geolocation data on Grindr users through a hidden but ubiquitous entry point: the digital advertising exchanges that serve up the little digital banner ads along the top of Grindr and nearly every other ad-supported mobile app and website. This was possible because of the way online ad space is sold, through near-instantaneous auctions in a process called real-time bidding. Those auctions were rife with surveillance potential. You know that ad that seems to follow you around the internet? It’s tracking you in more ways than one. In some cases, it’s making your precise location available in near-real time to both advertisers and people like Mike Yeagley, who specialized in obtaining unique data sets for government agencies.