A Monitor’s Ultrasonic Sounds Can Reveal What’s on the Screen

Researchers have demonstrated that they can discern individual letters on a display based only on the ultrasonic whine it emits.

The technique, presented at the Crypto 2018 conference in Santa Barbara on Tuesday, could allow an attacker to initiate all sorts of stealthy surveillance by analyzing livestreams or recordings taken near a screen—say from a VoIP call or video chat. From there, the attacker could extract information about what content was on the monitor based on acoustic leakage. And though distance degrades the signal, especially when using low quality microphones, the researchers could still extract monitor emanations from recordings taken as far as 30 feet away in some cases…