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

You probably assume that someone can only see what's on your computer screen by looking at it. But a team of researchers has found that they can glean a surprising amount of information about what a monitor displays by listening to and analyzing the unintended, ultrasonic sounds 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 .