Koobface computer worm that targets users of the social networking websites such as Facebook and MySpace. Reading backwards, you will realize that Koobface is a rewording of the word Facebook i.e Koob for Book and putting 'face' at the end instead of, the usual, at the beginning. Read more about Koobface by clicking here.
Koobface engineers have spoofed YouTube videos, attaching an image that encourages the reader to click on it. Once clicked, a message pops out wanting you to update your Flash Player in order to see the video. Once you click on it Koobface downloads into your computer start it's malicious attack.
The two images below shows how the Koobface mimics YouTube and install Flash Player windows.