There are quite a few options. What works for me is:
Downloaded Google toolbar with PopUp Blocker, and use Google as default
search engine- very effective.
Purchased AdAware Plus (freeware version is available, but without AdWatch).
It will detect and remove spyware, malware, etc. The Adwatch feature allows
you to setup your system so that no modifications to your registry are
allowed without permission.
Stop the Messenger service in Windows. If you are running XP, do a search
for "shootthemessenger"- it is a small program that will disable the service
on your computer (you really do want to do this- it can be done manually
from Computer Administration if you are familiar with it).
I also run Window Washer daily and have a program called RegCleaner which
will remove obsolete registry entries like those left over from programs
which have been removed from your computer.
Good Luck,
Fitz