I´ve been using Firefox for about 3 months now

I always ran Spybot Search & Destroy with IR6 and now also with FF

I am not so sure that I get fewer bugs than before.

But, to answer the original question, I think the lesson is clear: a good anti-vir, and a firewall...properly configured, combined with some decent clean-up software and from time to time an alternative scan.

Zone-Alarm is helpful, but as already mentioned, watch-out for conflicts.

My only protection nowdays is Kaspersky and the Windows-own firewall. I scan every day with Spybot or SE-Adaware and run CCleaner. Above all read the instructions and get online to read what the users say.

For a free anti-virus, there are several good options. I favour AVG. Others may recommend Anti-vir, or one or two others. Again, read about it...Google is your friend!