http://www.free-av.com/ has a completely free anti-virus program.
There is an online scan and repair program available at
http://www.pandasoftware.com/actives..._principal.htm , but I cannot comment on its quality (Panda is a respectable company, though).
http://www.safer-networking.org/ has the highly recommendable SpyBot which removes and blocks all spyware or adware.
http://www.kerio.com/kpf_home.html is a free and effective personal firewall recommended by people who know more about such stuff than I do.
[ August 23, 2003: Message edited by: Sharkû ]