A new version of an old computer worm has a nasty twist, anti-virus firm Sophos warned on Monday. The Rbot-GR worm can use webcams attached to infected computers to spy on users.

"More and more hackers are interested in spying on the people they manage to infect with their worms and Trojan horses," said Graham Cluley, senior technology consultant for Sophos. "In the workplace, this worm opens up the possibilities of industrial espionage. At home it is equivalent to a Peeping Tom who invades your privacy by peering through your curtains".

The worm, which is not widespread, uses network shares to propagate and affects only Windows PCs. It installs a backdoor Trojan horse on infected computers, software that gives other users remote control of the target computer, allowing them to spy through the webcam and potentially allowing them to steal passwords and other information as well.

"If your computer is infected and you have a webcam plugged in, then everything you do in front of the computer can be seen, and everything you say can be recorded," said Cluley.

"With many home users keeping poorly-defended PCs in their bedroom, there is considerable potential for abuse. The message is simple - keep your PC protected against the latest threats with anti-virus software and firewalls, and if in any doubt unplug your webcam when you're not using it," he added.

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