A virus dubbed as "Koobface" is infiltrating Facebook's 120 million users by using the social network's messaging system to infect PCs, and get credit card numbers.

This is the most recent attempt of hackers looking to take advantage of users on social network sites.

"A few other viruses have tried to use Facebook in similar ways to propagate themselves," Facebook spokesman Barry Schnitt said in an e-mail. He said a "very small percentage of users" had been affected by these viruses

"It is on the rise, relative to other threats like e-mails," said Craig Schmugar, a researcher with McAfee Inc.

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