Extraterrestrial search system Seti@home has been hit by hackers for the second time in two months, with the culprits cheating to get more data crunched in their own name.

The scammers have written a virus which infects internet users' machines, disables antivirus software and then downloads the Seti@home software, setting it up to crunch data for the virus writer's account.

The Seti@home client software crunches a block of data, received by radio telescopes looking for signs of extraterrestrial life, before returning it to the Seti@home processing centre.

Over three million people have signed up to search for aliens, and users who crunch the most data are featured as 'Cruncher of the Week'. It is most likely that the virus writer is trying to attain these lofty heights by cheating.

Most antivirus companies have released an update to thwart the virus, although the code is not thought to have infected many machines. Virus definition files have labelled it the 'Hyd' worm, which mass-mails itself via Outlook.

Separately, hackers broke into the Seti@home user database last month escaping with around 50,000 email addresses, a number of which were later subjected to major spam attacks.

The virus definition can be found here.