In a recently published paper, researchers at the University of Washington demonstrate that practically anyone can spend a little cash and track, in relatively real time, the location of a human target. That's digital surveillance, made available to any and all with money on hand, brought to the masses by your friendly neighborhood Silicon Valley disrupters.

The idea is straightforward: Associate a series of ads with a specific individual as well as predetermined GPS coordinates. When those ads are served to a smartphone app, you know where that individual has been.

"The first step to enable location tracking using ads is to obtain the target’s MAID [Mobile Advertising ID] by sniffing their network traffic (see below), which allows us to specify ads to only be served to the target device," explain the study authors. "Then we create a series of ads, each targeted at that MAID, but each also targeted at a different GPS location. This creates a geographical grid-like pattern of ads. Then we can observe which of these ads gets served, and this indicates where the target actually was."