Odd Behavior and Apparent Adware

I have been using NIS for about 10 months now, including the most recent upgrade to 2011.

 

My questions is about this:  I apparently have some adware that is not removable. I have run numerous full scans and the same popup windows still occur despite my having my popup blocker always set to 'On".

 

The popup windows are always related to whatever webpage I happen to be using at the time.  They are frequently an "free survey" offer, but often are just ads. A screenshot of one such popup is attached.

 

I have contacted my ISP (Yahoo) but they have been useless.

 

Has anyone else heard of this kind of popup?  If so, what can I do to remove it?