Not totally sure about this but it sounds like a virus to me; is it happening on any other sites? I'd run whatever virus scanner you have, just in case.
~ [Fa]mily~
"You may have Downs, but you get me up." - Hucota7
you can try the freeware version of malwarebytes ( http://www.malwarebytes.org/ ) for possible removal unless its a browser extention try what PTDx said
