 As users increasingly own networked devices such as smart phones, mobile devices collect and send more and more data. These devices typically contain a range of data-generating sensors, including GPS (location), movement sensors, and cameras, and may transmit the resulting data via the Internet or other networks. One particular example concerns location data. Many mobile devices have a GPS sensor that registers the user’s location, but even without a GPS sensor, approximate locations can be derived, for example by monitoring the available wireless networks. As location data links the online world to the user’s physical environment, with the potential of physical harm (stalking, burglary during holidays, etc.), such data are often considered particularly sensitive.