fastclick.net

A couple of time recently, as I was minimizing some windows while either here in the Dell forums, or in the MSN flight sim group, that a rectangular box is on the screen...not squarish like a pop up box. It has a label at the top that says it is fastclick.net. I am sure this badware and can't understand what might cause it to appear.

 

When I go to Internet Options it is blocked both in the Restricted Sites>Security tab and the same under the Privacy tab. No other problems, and all scans come up clean...MS beta, Ad-Aware, Spybot. Any ideas on this one?