You, sir, have adware. I feel for you.
There's a few things you can do. If you're lazy, and/or have no know-how, you can download an adware remover like Spybot. I, however, find those programs more annoying than the adware itself. So, if you're like me and you don't like that option, you can scour your registry for the adware and remove it. The most popular/frequently appearing adware are Gator (GMT or GT) and Wildtangent (WT or WildT). Search your registry and/or your C: for signs of these evil, evil little programs. If and when you find them, you know what to do. DELETED!!