A worm, dubbed Cellery-A (W32/Cellery-A), which poses as a playable version of the classic Russian computer game Tetris has been detected in the wild, security experts have warned.

The Cellery worm, which gets its name from a message it displays saying 'Chancellery', makes changes to Windows settings to ensure that it automatically runs when the operating system starts up.

While the Tetris-like arcade game is running, the worm plays a MIDI music tune, and searches for other network drives and attached computers to also try and infect.

"This worm puts up the Tetris game as a smokescreen while 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 is simply a new game that has been installed - rather than something that should cause concern."

Sophos reported that Cellery is not the first virus to allow infected users to play games on their PCs. The Bibrog worm posed as a shooting game, while the Coconut worm, written by the female Belgian virus writer Gigabyte, gave users the opportunity to throw coconuts at photographs of members of the computer security community.

Although there have only been a small number of reports of the Cellery worm, Sophos recommends computer users ensure their anti-virus software is up-to-date.