Well, according to FB, it does. :wink:

...in the past three months we have helped clean up more than 2 million people's computers that we detected were infected with malware when they connected to Facebook. In these cases, we present a cleanup tool that runs in the background while you continue using Facebook, and you get a notification when the scan is done to show you what it found.
But as I don't use FB, I can't comment on the quality of this service...