A computer virus dubbed ‘Koobface’ is being spread through the messaging system of social networking sites, like Facebook and MySpace, posing to the users a threat similar to other malware attacks over the years. Users whose computers are infected may have their credit card numbers stolen or their searches on Google, Yahoo and MSN diverted to deceptive Web sites.

Since social networking sites allow messages only between fellow members who are confirmed friends, it is through messages sent from those with the virus-infected computer that Koobface is spread.

Messages arrive in Facebook inboxes with titles like “you look just awesome in this new movie” or something similar, and direct readers to another Web site to supposedly watch the clip. Once they are on the video site, another message says an update of Flash is needed before the video can be displayed. The viewer is prompted to open a file called flash_player.exe, and downloading the software infects the victim’s computer with the virus.

Craig Schmugar, threat researcher for McAfee Avert Labs, said that the prompt for a new player should be a warning, adding: “The messages you tend to get from these sites don’t look quite right.” Schmugar said this attack is similar to e-mail attacks a decade back in that Koobface is using infected friends lists, reminiscent of early mass-mailing worms. As was the recommendation then, he advises users not to open any unexpected e-mail attachments, even if they are from someone they know.

Barry Schnitt, a spokesman for Facebook, in Palo Alto, said: “We’re working quickly to update our security systems to minimize any further impact”, and added that Facebook has posted instructions on how to remove the infection.