Try searching 'iTunes" in Google and the top sponsored result is something called itunes,download-new.com. Whatever you do, don't go there. Because it is crawling with a whole lot of malware.

The clever, and evil ad placement is why you're probably getting tons of pop-up ads and other computer crippling type of software.

Even a search on Bing for "iTunes" first showed no trickery, then showed much trickery: