Back in the day, Mr. Wim Van Eck "proved it was possible to tune into the radio emissions produced by electromagnetic coils in a CRT display and then reconstruct the image," effectively rendering the images on a distant monitor without the user knowing. A modern hacker has found that the methodology used in 1985 can still be just as useful today - on laptops and flat panel LCDs. Markus Kuhn has discovered that by tuning into the radio emissions produced by the cables running into a monitor, hackers can garner the pixels one at a time, and carefully stack them together to form a picture of someone else's screen.
Reportedly, Markus was able to "see a PowerPoint presentation from a stand 25 meters away" and he also noted that laptops with metal hinges were particularly good targets as they tended to broadcast the necessary signals quite well.
My theory has always been - if someone wants your information - they will get it BUT the average person, even the most talented hacker, doesn't know how.
Not that anyone is doing this - but this could be a way to hack Macs some time in the future. I wonder if the new LED backlighting for LCDs coming from Apple will be better and make this more difficult or impossible.