Microsoft is working with Facebook to keep the persistent Koobface virus off the popular social-networking site, the companies said on Thursday.
"In working with Facebook, we were able to add detection of Koobface to our Malicious Software Removal Tool (MSRT), which checks computers running Windows software to detect and remove viruses," Jeff Williams, a principal group program manager for the MRST, wrote in a guest post on the Facebook Blog.
The MSRT has removed Koobface nearly 200,000 times from more than 133,600 computers around the world just in the past two weeks, he wrote.
Koobface is a mass-mailing virus that arrives in Facebook users' in-boxes announcing a message like "You look funny in this new video." Clicking on the link takes recipients to a Web site where they are prompted to download a Trojan masked as an Adobe Flash update. The Trojan could allow an attacker to remotely steal a victim's Facebook password and other information or even use the computer to launch attacks on other computers.
Koobface has been around since August mostly targeting social networks, and a variant that targets only Facebook users surfaced in December. Facebook has been hit by at least one other version since then.
Details on how to protect against Koobface are on Facebook's security page.