A worm which poses as a version of classic computer game Tetris is spreading across the net. The Cellery worm spreads across insecurely configured network shares and distracts infected users with a Tetris-like arcade game and a MIDI music tune while it scours network drives and attached computers for fresh victims. Few copies of the worm have been seen, so Cellery is a curiosity rather than as a serious risk, right now.

"This worm puts up the Tetris game as a smokescreen as it tries to hop from computer to computer across your network," said Graham Cluley, senior technology consultant for Sophos. "If your company has a culture of allowing games to be played in the office, your staff may believe this simply a new game that has been installed - rather than something that should cause concern."

Packaging malware in games represents is an unusual but not unprecedented tactic for virus authors. The Bibrog worm posed as a shooting game, while the Coconut worm, written by the female Belgian virus writer Gigabyte, gave users the chance to throw coconuts at pictures of members of the computer security community, including Sophos's Cluley.

Happy ‘Nude’ Year

Another worm doing the rounds this week demonstrates that virus writers are inventive when it comes to social engineering tricks. The Wurmark-D worm offers prospective victims an unconventional Happy New Year message in the shape of a photograph of naked bodies. Infected emails pose as seasonal greetings with a "screensaver" attachment that launches the image as well as infecting any Windows PC it is launched from. Upon infection the worm will search infected hard disks for email address to send itself to as well as disabling any antivirus protection. Wurmark-D has found few victims and is rated as a low risk.

Wurmark-D and Cellery infect Windows PC onlys, as is the norm. Standard defensive precautions apply: avoid opening unsolicited attachments, update AV tools to detect the worms, apply the latest Microsoft security patches and use a personal firewall. If you think your PCs might be infected with a virus then our guide to cleaning up PCs may come in handy. ®

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