Yeah the format would be the best medicine, however I just formatted this drive like a week ago.
I dont have yahoo messenger at all though no, just MSN Messenger, but that hasnt ever given me problems before.

This one has sort of embedded itself somewhere, i first noticed it when I was playing one of those pointless flash animation games on the web, once i closed it down I had all these weird shortcuts that were installed on my desktop, and ever since...non stop pop ups.

This particular one also recognises afew variations when you type different things to search in google for example.
like if on google i want to search for "Microsoft" and hit enter, a pop up will come up showing a bogus Microsoft update site, and it'll ask me if i want to update and to select yes. Did the same thing when I selected the automatic updates option from windows also. To my surprise I saw 2 update sites, one was the real thing, the other was the fake.
and usually works with other search queries aswell, I also tried Symantec, Adobe. all of which had "bogus" sites related to them.
But yeah, obviously whenever you search for something on google, you dont get your results taking you to a specific site as a pop up.