virus or an ad?

every once in awhile when I go to a certain site, I will get a pop up box saying something about "possible virus" and to run a scan. It is not my Norton requesting this, but some odd/weird antivirus product.  my broswer window ( IE7) will close leaving the pop up box in place. I close this out using task manager.

 

When I check my browsing history, there will be this item noted andoscan.info

 

I run a Norton scan and it finds nothing

I also run spybot S&D and windows defender ( I use as on demand scanners) and they find nothing either

 

I have talked with a few people who use the same site as I do and they say they get the same pop up every once in a while

As I said it is not all the time

 

So does it sound like an ad or an infection?

 

[edit:Please do not post links to potentially dangerous websites.]

Message Edited by shannons on 09-05-2009 01:21 PM