When you have millions of users, 175 million to be exact, it makes for an easy target for Malware authors and Hackers to invest time and energy. Facebook has been under fire lately with the well known Koobface worm. The Koobface worm finds the social-networking cookies, it makes a DNS query to check IP addresses that correspond to remote domains. Trend Micro explains that those servers can send and receive information about the affected machine. Once connected, the malicious user can remotely perform commands on the victim’s machine.

According to Michael Argast, a security analyst at Sophos. “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.

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.

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.

“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.”

Facebook will not be the only target so don’t get too comfortable if your on another network. StumbleUpon and Digg have millions of users and these Malware authors will have no problem testing those waters.