"Many computer users have been conditioned not to open an attachment from an e-mail or click a link found within, but won't think twice about checking out a hot new video linked to by a trusted friend on Facebook," Argast said.


Malware authors are investing more energy in Facebook and other social-networking sites because that effort pays off, according to Michael Argast, a security analyst at Sophos. Facebook alone has more than 175 million users, which makes it an attractive target.


"I would expect to see more attacks on Facebook," Argast said. "As long as this is a successful propagation method, the bad guys will double down and invest more. They are entirely motivated by financial gain. If it pays, they'll continue to romp in your social playgrounds."


Argast said people can protect themselves by running up-to-date antivirus software, restricting which Facebook applications they install, thinking twice before clicking on links from friends and never, never installing a codec from some random Web site in the hopes of catching some celebrity in a compromised situation.


Argast called the Koobface worm a mix of something old and something new. The new is using social networks as a method to spread malware. The old is using fake codec Trojans linked to a saucy video to induce the user to install the malware.