Spies attracted to the light

Is this component betraying your organisation?

Flickering computer screens and status lights on computer hardware could be giving away important information about the data they are processing.

In separate research papers, scientists have demonstrated how to decode the information hidden in the flickering lights.

One of the reported techniques can even read information from light reflected from a computer screen on to nearby walls.

But experts say there is no need to start putting sheets over computer monitors or tape over blinking lights because there are easier ways to spy on computer users.

Flash forward

Almost all pieces of computer hardware have light-emitting diodes that let their owners know if the device is powered up, passing data or sitting idle.

But scientists have discovered that, on some devices, the sequence of flashes acts like Morse code and can reveal the entire stream of data passing through the hardware.

Joe Loughry, a programmer from Lockheed Martin Space Systems in Denver, US, and David Umphress, a professor from Alabama's Auburn University, also US, have demonstrated how to convert the flashing lights into readable data.

Techniques revealed in the research show how to read data from a flashing LED up to 20 metres away. But the researchers point out that not all devices are equally susceptible to tapping in this way.

Only the flashing diodes on some dial-up modems and internet routers blink in a way that can reveal the data passing through their devices.

The research has been submitted to a journal called Transactions on Information and Systems Security.

Screen grab

For his part, Markus Kuhn, a researcher at the University of Cambridge's computer science laboratory in the UK, has found that the flickering of a computer screen can also be exploited to surreptitiously gather information.

Mr Kuhn has found that the intensity of light given off by computer monitors, but not flat panel displays, is related to the characters being displayed on that screen.

Using sensitive detectors it is possible to reconstruct the on-screen information simply by capturing the changes in the strength of the light.

The technique even works when the flickers are being reflected off a nearby wall.

Mr Kuhn will be presenting his research findings during the IEEE Symposium on Security and Privacy to be held in California from 12-15 May.