A worm that plays video game Tetris with victims as it attempts to further contaminate networks has infected a small number of PCs, antivirus firm Sophos warned Wednesday.

The worm, known as Cellery.A, uses a playable version of the Russian video game to attract victims. While people play Tetris, the worm attempts to spread to networked hard drives and other accessible systems on a company's network that use the Microsoft Windows operating system, the firm stated in an advisory.

"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," Graham Cluley, senior technology consultant for Sophos, said in a statement.

Games are an uncommon way to attempt to spread code. Shooting games and a coconut-throwing game have both been carried by worms to attract potential victims. More than four years ago, another Tetris-playing worm spread through chat channels and carried a working copy of the game.

Sophos did not mention the previous Tetris worm in its advisory, and it's unknown whether the two Tetris-playing programs are related.

The first computer virus to affect a general-purpose computer system was also linked to a game. Virus-like program Pervade was created in 1975 by John Walker - who later founded Autodesk - as a means of distributing the game "Animal" on UNIVAC systems. The virus spread through files transferred between systems on magnetic tapes.

Sophos has released its latest antivirus signatures to detect the Cellery worm:
http://vil.nai.com/vil/content/v_98906.htm