Users of social-networking Web sites have been warned to be on their guard after Facebook was targeted by a virus dubbed "Koobface."
The Koobface video virus uses the social network's messaging system to infect computers and then tries to gather sensitive information such as credit card numbers.
It is the latest attack by hackers looking to cash in on the popularity of social-networking sites where e-mails and messages supposedly from friends are more likely to be opened, exposing the user to the virus. Facebook has more than 120 million users.
"A few other viruses have tried to use Facebook in similar ways to propagate themselves," Barry Schnitt, a Facebook spokesman, said in an e-mail.
He said a "very small percentage of users" had been affected by these viruses.
The Koobface virus spreads by sending notes to friends of someone whose PC has been infected.
The messages, with subject headers like, "You look just awesome in this new movie," direct recipients to a Web site where they are asked to download what it claims is an update of Adobe Systems' Flash player.
If they download the software, users end up with an infected computer, which then takes users to contaminated sites when they try to use search engines from Google, Yahoo, MSN and Live.com, according to security experts.
Dozens of versions of the virus have been around since August. Users of MySpace were infected users at one point.