Beware of ads that use inaudible sound to link your phone, TV, tablet, and PC

Privacy advocates are warning federal authorities of a new threat that uses inaudible, high-frequency sounds to surreptitiously track a person's online behavior across a range of devices, including phones, TVs, tablets, and computers. The ultrasonic pitches are embedded into TV commercials or are played when a user encounters an ad displayed in a computer browser.
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