Not everyone who is your friend on Facebook is really your friend. In what can best be attributed to the growing popularity of social networks, hackers have inundated sites like MySpace and Facebook with worms designed to take control of an unsuspecting user's computer.

While Facebook and MySpace have been ramping up security efforts, the worm attacks highlight the vulnerability of any social network's most valuable asset: trusting users.

"Users are very trusting of messages left by 'friends' on social networking sites. So the likelihood of a user clicking on a link like this is very high," said Alexander Gostev, senior virus analyst at computer security firm Kaspersky Lab.

The worms, which tell a user that they've been caught on a hidden camera or promise video footage of Paris Hilton tossing a dwarf, take users to YouTube-style sites that look real, but in fact serve as launching pads for the installation of viruses.

For both Facebook and MySpace, which are fighting it out for supremacy, the viruses represent a significant threat because if left unchecked they could undermine the value of friending on the sites. That would then put a crimp in their plans to monetize the traffic.