Google has banned an army of Android apps that use ultrasonic sounds to spy on users without their knowledge.

The moves comes after researchers revealed that hundreds of Android applications are embedded with ultrasonic cross-device tracking technology that pick up inaudible 'beacons' emitted from advertisements.

This allows marketers to create personalised ads based on your interests, as they are able to determine your location and what activities you may be engaged in.

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Google has banned an army of Android apps that use ultrasonic sounds to spy on users without their knowledge (stock image of the Galaxy S8 smartphone)

HOW YOUR DEVICES COULD BE SPYING ON YOU Inaudible signals could be tracking your TV and web surfing habits more closely than ever before. Researchers revealed that hundreds of Android apps are embedded with ultrasonic cross-device tracking technology that pick up inaudible 'beacons' emitted from advertisements. This allows marketers to create personalised ads based on your interests, as they are able to determine your location and what activities you may be engaged in. These signals can be picked up by a range of devices, including phones and TVs. Signals are sent without the user's permission or knowledge. Advertisement

'A recent practice embeds ultrasonic beacons in audio and tracks them using the microphone on mobile devices,' reads a study from Braunschweig University of Technology, Germany.

'This side channel allows an adversary to identify a user's current location, spy on her TV viewing happens or link together her different mobile devices'.

While conducting their investigation, the team found 234 Android apps were made using the publicly available tracking software.

And these apps were found to listen 'in the background without the user's knowledge'.

The researchers from Braunschweig University of Technology found many of the apps that contain the code were developed for large companies such as McDonald's and Krispy Kreme.

The app ShopKick, which rewards users with discounts, was found to be one of the spy apps that monitors the user's location.

Researchers have discovered hundreds of Android applications are embedded with ultrasonic cross-device tracking technology (stock image)

Instead of tracking the user with the smartphone's GPS it uses the audio beacon emitted from the loudspeakers positioned at the entrance of a store to determine whether the consumer had walked into the store.

Game apps were also found to partake in this 'threat to privacy'.

ZDNET reported that games, such as Pino Henyo, are designed to open a user's smartphone microphone without them knowing and listen for ultrasonic tones.

But Google has now announced that all the apps discovered in the study have been either suspended or updated to meet privacy policies, according to CBS News.

They added that apps must now ask users' permission in order to use ultrasonic beacons.