Troublesome Popup Advertisements

I've been experiencing quite the annoying pop up. These aren't the popups that are associated with websites, but rather they popup at any given time while I'm on my computer all on their own.

 

They're advertisements about stupid videos, porn, where to get prescription drugs etc.. but they all come with a link to click on to 'Scan your computer for spyware problems!' Naturally I don't click on that nonsense.

 

On my own I've ran Symantec which found no viruses, SpyBot which finds nothing wrong with my registry, however SpyWare Doctor has removed over 200 infections, yet for some reason at least six of them keep reinstalling themselves no matter how many times I run SpyWare Doctor after I reboot my computer. Does anyone have any idea what keeps reinstalling itself and bombarding me with these annoying advertisement popups?