An investigation details Webloc, an ad-based geo surveillance system providing access to a constantly updated stream of records from up to 500M mobile devices (The Citizen Lab)

The Citizen Lab:
An investigation details Webloc, an ad-based geo surveillance system providing access to a constantly updated stream of records from up to 500M mobile devices  —  Location data collected from mobile apps and digital advertising can reveal habits, interests and almost any other aspect of someone's life.