Radiation from PCs can be used for spying


In a computer, some of the most powerful radiation emanates from the monitor, a cathode-ray tube in which electron guns fire streams of electrons more than 60 times a second to produce the images displayed. That bombardment produces wave frequencies, some of which overlap with the familiar VHF and UHF television bands.

In short, the invisible, information-bearing radio waves from a monitor are remarkably similar to a broadcast TV signal. A spy's scanner need only tune in the waves and process them line by line to replicate the image on the original screen.