Late Friday afternoon, Pacific Time, the computer identified as the command-and-control server used to send instructions to infected Koobface machines was offline. According to Nart Villeneuve the chief research officer with SecDev Group, the server was one of three Koobface systems taken offline Friday by Coreix, a U.K. Internet service provider. "Those are all on the same network, and they're all inaccessible right now," Villeneuve said Friday evening.

Coreix took down the servers after researchers contacted U.K. law enforcement, Villeneuve said. The company could not be reached immediately for comment.

The takedown will disrupt Koobface for a time, but for any real effect, much more will have to happen. Machines that are infected by Koobface connect to intermediary servers -- typically Web servers that have had their FTP credentials compromised -- that then redirect them to the now-downed command and control servers.

Friday's takedown is part of a larger operation that first started two weeks ago. Villeneuve and his team have notified the ISPs about the compromised FTP accounts, and they've also tipped off Facebook and Google to hundreds of thousands of Koobface-operated accounts.

The Facebook accounts are used to lure victims to Google Blogspot pages, which in turn redirect them to Web servers that contain the malicious Koobface code. Victims are usually promised some interesting video on a page designed to look like YouTube. But first they must download special video software. That software is actually Koobface.