Acoustical spying

Computer scientists at the

have taken several 10-minute sound recordings of users typing at computer keyboards, fed the audio into a computer, and used an algorithm to recover up to 96% of the characters entered.

"It's a form of acoustical spying that should raise red flags among computer security and privacy experts," said Doug Tygar, UC Berkeley professor of computer science and information management.

"If we were able to figure this out, it's likely that people with less honourable intentions can - or have - as well."

What makes the technique feasible is that each keystroke makes a relatively distinct sound, however subtle, when hit. Typical users type about 300 characters per minute, leaving enough time for a computer to isolate the sounds of individual keystrokes and categorize the letters based upon the statistical characteristics of English text. For example, the letters "th" will occur together more frequently than "tj," and the word "yet" is far more common than "yrg."