An increasing number of Android applications are attempting to track users without their knowledge, according to a new report. Over recent years, companies have started hiding “beacons”, ultrasonic audio signals inaudible to humans, in their adverts, in order to track devices and learn more about their owners. Electronic devices equipped with microphones can register these sounds, allowing advertisers to uncover their location and work out what kind of ads their owners watch on

TV and which other devices they own. The technique can even be used to de-anonymise Tor users.“Throughout our empirical study, we confirm that audio beacons can be embedded in sound, such that mobile devices spot them with high accuracy while humans do not perceive the ultrasonic signals consciously,” reads the report from researchers at Technische Universität Braunschweig in Germany. READ MORE