There is a malicious video on some MySpace pages that changes people's profiles when played, embedding itself and adding links to fraudulent Web sites:

The video is a rigged QuickTime file that exploits a MySpace vulnerability and support for JavaScript in Apple Computer's embedded media player, Web security firm Websense said in an alert posted on Friday. When played by a MySpace user, the video adds itself to the user's MySpace page and replaces the links on the user's profile with links to phishing Web sites, Websense said. Phishing sites are fraudulent sites that attempt to trick people into giving up sensitive information such as log-in credentials.

Update: MySpace has asked Apple to fix the flaw in QuickTime so it can't be used in attacks against MySpace visitors. Apple said it has provided MySpace with the temporary fix.