High-Frequency Sounds Embedded in Ads Used to Track Users Across Devices

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Inaudible sounds, the future of online user tracking
CDT (Center for Democracy & Technology) has alerted the FTC (Federal Trade Commission) about the existence of a privacy-intrusive, hidden high-frequency audio cross-device tracking technology.

According to an official complaint filed by the CDT, the privacy watchdog is tattling on advertisers like SilverPush, Drawbridge, and Flurry, online companies that deploy ads that squeal high-frequency sounds from the devices they’re loaded on.

The CDT says that these ultrasonic sounds scan the room for other devices like phones, tablets, TVs, computers, and wearables, effectively tying their presence to a browser cookie, an IP, and indirectly a user.

Whenever the device owner accesses a page with an ad from these companies from other handsets, the ad network will be able to recognize him based on the device’s fingerprint in their database and the presence of some tracking code left behind by the ultrasonic sounds emanated from previous visits via other nearby devices.


The entire technology is quite questionable and would allow advertisers to track users even if they don’t want to be tracked. Additionally, the practice also doesn’t include any options that users can tick and be left out of the tracking program.

A questionable practice, unknown to many, even the FTC

While advertisers are actively interested in delivering more efficient ads, users may not see it as such. A tracked user may not want personal Web browsing and TV watching habits stored in such fine detail on an advertiser’s unsecure server somewhere online.

The CDT says that as of April of 2015, SilverPush’s ultrasonic tracking software (SDK) has been embedded in 67 mobile apps, allowing the company to track 18 million smartphones and an unknown number of nearby devices.

“CDT is unaware of the existence of any current process for users to identify when probabilistic tracking is being used or meaningfully opt out. This represents a significant infirmity for any type of privacy protection,” say CDT representatives. “As such, the entities engaged in probabilistic tracking merit careful scrutiny  from the FTC.”

The FTC has officially reviewed CDT’s complaint today, and will be making a formal announcement in the following days.



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