Hi Suzy,
I did a bit of a google search and found acouple of sites that show how to tackle the problem. Some look very complicated, others not so.
I think this one might help you along:
http://guides.yoosecurity.com/how-to...-removal-help/
Do a ggogle search for " how to get rid of adserverplus popups"....
Looks like a doozy!
Good luck
Bartman