There seems to be a new virus around called Actns/Swif.T which comes through embedded YouTube videos in blogs and elsewhere.
I first came upon it this morning on someone else's blog, when my antivirus highlighted it and deleted it. I was shocked to find my blog was also affected this evening.
I am gradually working back and removing all the YouTube embeds, fortunately I don't have too many, but it is possible you may encounter this virus on an older page here or elsewhere. Google it for more info, I'm not techie enough to understand the implications should it get past your antivirus.
Update: It appears that the situation is not as serious as it seemed. Although it is a very real virus and nasty if you click on the link it delivers, apparently yesterday Computer Associates antivirus, which I have, was throwing up false positives on any page containing embedded YouTube videos. They seem to have fixed their virus definitions now. But still watch out for the virus!