Catalin Cimpanu, writing for BleepingComputer: A team of researchers from the Brunswick Technical University in Germany has discovered an alarming number of Android apps (234, to be exact) that employ ultrasonic tracking beacons to track users and their nearby environment. Their research paper focused on the technology of ultrasound cross-device tracking (uXDT) that became very popular in the last three years. uXDT is the practice of advertisers hiding ultrasounds in their ads. When the ad plays on a TV or radio, or some ad code runs on a mobile or computer, it emits ultrasounds that are picked up by the microphone of nearby laptops, desktops, tablets or smartphones. SDKs embedded in apps installed on those devices relay the beacon back to the online advertiser, who then knows that the user of TV "x" is also the owner of smartphone "Y" and links their two previous advertising profiles together, creating a broader picture of the user's interests, device portfolio, home, and even family members.