Although at the moment it has only been proven upto 15m (Metres) away
Anyway here is the story and a quote below - http://news.bbc.co.uk/1/hi/technology/8147534.stm
Power sockets can be used to eavesdrop on what people type on a computer.
Security researchers found that poor shielding on some keyboard cables means useful data can be leaked about each character typed.
By analysing the information leaking onto power circuits, the researchers could see what a target was typing.
The attack has been demonstrated to work at a distance of up to 15m, but refinement may mean it could work over much longer distances.
Edited by woodyblade, 13 July 2009 - 11:24 AM.