Two things.. First, re-set the browser you're using. A re-set will remove your profile from your browser and take it back to it's original state. Unfortunately, you didn't give us the browser you're using so we can't give you specific on how to reset the browser but a quick check on Google will tell you how.

Next, because malware is the most like culprit/cause for this stuff, do some additional scans by following the instructions in the link below. Follow them to the letter, in the order given. It may take a while to finish all the scans, but it will get rid of the junk.

“Expand” the post titled: "Please try this" at the link below:
http://www.cnet.com/forums/post/f742c795-5881-433b-a29b-6d758efe5cd3/

Hope this helps.

Grif