The Koobface worm which has plagued the Facebook social networking site during the past week, is now targeting MySpace, Bebo, and other sites as well, security researchers warn.

Researchers at security vendor F-Secure said yesterday in a blog about the Koobface worm that the new infection is designed to spread to other popular social networking sites, including MyYearbook.com, BlackPlanet.com, and Friendster.com.

Koobface, which was first reported last week by McAfee Avert Labs, uses Facebook's private messaging system to spread itself across the social networking site. Facebook users receive a message from an infected profile that offers them a video link paired with the message, "You look just awesome in this new movie." The link takes users to a separate Website that recommends installing an update to watch the video. But the download is actually the virus itself, and installing it leads to another infected computer.

The new discovery is actually a resurgence of Koobface, which was reported by Kaspersky Labs in July. As part of their malicious payload, the worms transform victim machines into zombie computers to form botnets, Kaspersky said.

"Facebook is already aware of this [new] threat and is purging the spammed links from their system. But with dozens of Koobface variants known to exist, the situation is likely to get worse before it gets better," Craig Schmugar of McAfee Avert Labs wrote on the company's blog. "It's important to note that spammed links leading to Koobface are likely to come from infected friends, reminiscent of early mass-mailing worms."

The worm raises the spectre of large-scale viruses that attacked across the Internet in the past decade, experts say. In recent years, such viruses and worms have waned as attackers favored more targeted exploits that created less attention.

But with the ever-increasing effort to find zombies to work in botnets, such large-scale attacks are making a comeback, experts say. Social networks are an obvious target for such attacks because users are more likely to click on links or be duped by messages if they come from individuals they believe to be "friends," they say.

Facebook says it is deleting content generated by the worm, and officials say the social networking site has "again contained" the worm. The company also is posting updates to the Facebook security page and is publishing best practices to help users avoid phishing attacks.

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