Some sneaky little blighter of a software has somehow snuck into the workings of my PC. I know it's the PC as I have no problems on my laptop or at work.
Now, when I logon to any website, I get a page full of blue, underlined words. When I hover over them I get a pop-up advert.

Like so...
Any ideas what this bloody software is? I've obviously anti-virus'd and anti-spywear'd and gone through my Control Panel, but I cannot seem to find it.
Any ideas?