for those that won't RTFA...
Apparently some sort of relatively aggressive virus is affecting certain embedded YouTube videos. Some are saying it affects IE and Firefox users, while others say it’s only going after IE. The virus is called Actns/Swif.T and seems to contain a redirect to a phishing website embedded within a SWF file.

The site apparently installs Antivirus 2009, which is malware. We’ll pull our most recent YouTube embeds, but be careful because this one appears to have just broken out today. If you find yourself being automatically redirected or experience other weird pop-ups, especially for something called Antivirus 2009, don’t click on anything.
so... DO NOT USE anything called Antivirus 2009

(and seriously... why use free AV software? you know those companies pay their people somehow, right??)