A stealthy side-channel tactic for digital surveillance has been uncovered, which allows an attacker to “hear” on-screen images.
According to a team of academic researchers from Columbia University, the University of Michigan, University of Pennsylvania and Tel Aviv University, inaudible acoustic noises emanating from within computer screens can be used to detect the content displayed on those screens. This includes the text on the screen of a computer, or website content that a user may have opened on their desktop. It can also be used to monitor users’ input into on-screen virtual keyboards. This can all be detected and recorded by the microphones built into laptops and webcams; the subtle acoustic signals also can be recorded by a smartphone or speaker placed on a desk next to the screen, or from as far as 10 meters away using a parabolic microphone.