Tracking Caucusgoers By Their Cell Phones (schneier.com)

Okian Warrior writes: Dstillery gets information from people's phones via ad networks. When you open an app or look at a browser page, there's a very fast auction that happens where different advertisers bid to get to show you an ad. Your phone sends them information about you, including, in many cases, an identifying code (that they've built a profile around) and your location information, down to your latitude and longitude. On the night of the Iowa caucus, Dstillery flagged auctions on phones in latitudes and longitudes near caucus locations, some 16,000 devices. It then looked up the characteristics associated with those IDs to make observations about the kind of people that went to Republican caucus locations versus Democrat caucus locations. It drilled down farther by looking at which candidate won at a particular caucus location.