In short, Koobface will make auto messages and sends it to your friends. The message have the link from other sites containing this worm. Once it was clicked and downloaded, then it will infect your friend's computers and repeat the cycle all over again.
Please do note that one of the variants of this virus is in the form of fake YouTube Videos.
Source: Yahoo Tech News
Concerning this virus, I don't know if this virus is similar to the spam that we I used to receive in our Friendster account. In my experience, those video clips will be posted in my “comments”. The video picture usually has a lady wearing an underware garments acting to change her clothes. And once you click on the video, it will bring you not in YouTube site but in another site.
I received those comment messages almost all the time before. And when I tried to delete them, it will reappear again. To my surprise, some of them were posted automatically in my profile.
If these kinds of spam messages is related to Koobface, I don't know. But I think the actions is very similar to what has been reported.