The adware and anti-virus programs will not stop the latest CWS or iSearch variants. If you get one, you'll know it because your browser will be hijacked.
General fyi: the Congress is currently debating between two bills designed to criminalize spyware/adware/malware and they should get something passed soon. Not nearly as soon as they should've, though!
>>You just have to invest in a good Adware/virus program...in fact maybe two or three and scan every day.<<
I updated My FR homepage because I get asked these questions every day.
The biggest prevention is Firefox. The next is spyware blaster. The last is an ad remover as some infections come in that way. I use Ad-Muncher and I've tried them all. http://www.admuncher.com
Try it for 30 days for free. I bought two copies, worth every penny.
-Mal