There are quite a few 'pop-up killers' around and most do a good job of stopping the windows from opening.
These programs can give the users a false sense of security.
To keep this machine clean I use the fiollowing:
BlackIce Firewall
PC-Cillin 2000 anti virus
SpyStopper
I bought this last piece of software on 23rd August and so far it has stopped:
Ads 17,306
Bugs 3,150
Cookies 4,987
Scanners 1
Scripts 564
Spyware 2
Stylesheets 103
Websites 9
from getting into my pc.
As a customer I can say it is well worth the cost.
On top of this give the system a scan with ad-aware every 2 weeks and no problems.