Report: Android Apps Using Hidden Advert Audio Signals to Spy on Users

A report claims that ultrasonic audio in advertisements is being used to activate user tracking features on Android apps.

A new report from researchers at Technische Universität Braunschweig in Germany claims that in recent years companies have hidden ultrasonic audio signals known as “beacons” in advertisements that activate tracking features in Android devices and have allegedly used these features to gain information on their owners.

The report states, “A recent practice embeds ultrasonic beacons in audio and tracks them using the microphone of mobile devices. This side channel allows an adversary to identify a user’s current location, spy on her TV viewing habits or link together her different mobile devices.”

The report also claims that the issue is quite widespread, having been monitored in as many as seven cities:

Our findings confirm our privacy concerns: We spot ultrasonic beacons in various web media content and detect signals in 4 of 35 stores in two European cities that are used for location tracking. While we do not find ultrasonic beacons in TV streams from 7 countries, we spot 234 Android applications that are constantly listening for ultrasonic beacons in the background without the user’s knowledge.

The report hasn’t acknowledged which applications are using this beacon listening method but did state that many of the apps have millions of downloads and are linked to “reputable companies” such as McDonald’s and Krispy Kreme.

It is noted, however, that the device owner must have the app open in order for the “beacon” to be listening to the advertisement. Currently, devices can not start automatically listening without some interaction from the device owner.