By monitoring the flashes of LED lights on electronics equipment and the indirect glow from monitors, scientists in the United States and the United Kingdom have discovered ways to remotely eavesdrop on computer data.

Optical signals from the little flashing LED (light-emitting diode) lights, which are on everything from modems to keyboards, can be captured with a telescope and processed to reveal all the data passing through the device, according to Joe Loughry, a computer programmer at Lockheed Martin Space Systems.

?It requires little apparatus, can be done at a considerable distance, and is completely undetectable,? he says. ?In effect, LED indicators act as little free-space optical data transmitters, like fiber optics but without the fiber.? He can read a strong optical signal from about 22 yards, using optical sensor equipment.

Loughry says not every LED-enabled device is being watched. Spies are interested in the equipment used in automated teller machines at banks rather than home Internet connections.

?It is interesting to walk around downtown at night in a large city and look up at the glass windows and you see a lot of computers,? he says. ?I?ve seen racks of equipment with LEDs on them visible from the street. That?s kind of what got me to pursue this.?

When he?s asked how this could have been overlooked for so long, he says, ?I guess nobody ever looked at it before. I was working very late one night and waiting for a long file transfer to complete and I was just staring at these lights on the front of the modem and started to wonder if there was anything there.?

You can protect your privacy by locating your equipment away from windows, putting black tape over LEDs or de-activating them when they?re not in use. Equipment manufacturers also can modify their devices.

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