ZoneAlarm was so good as freeware that I bought the more feature-rich version. It is, by the way, the only freeware firewall-style software I know of.
I use Norton Anti-Virus. Yes, I know it’s not free, but it’s reasonably-priced, well-supported (usually) and very reliable. As a result of NAV and some careful use of the Internet, I have (so far) avoided viruses. I do run it constantly, though; on my work computer I run it every night. That’s certainly overkill, but then I don’t have to remember if I’ve run it or not, and I can then rely on my work computer as much as I do on my work telephone!
LavaSoft has a free version of its AdAware spyware-checking software.
I’m sure you can find free anti-virus software, but it may not be as good as NAV at protecting you.
The best protection is social engineering:
[li]Develop good passwords and change them regularly.[/li][li]Don’t share passwords with anyone.[/li][li]If you have to write down passwords, protect them with other passwords you can remember.[/li][li]Keep your records and work desk secure. Never walk away from your computer without at least “software” locking it.[/li][li]Don’t let web sites set “remember me” cookies on your laptop.[/li][li]Get a program like Quicken and use it to check your credit card and bank balances on a daily basis. Even though crooks are getting through to credit data these days, you’re still much more exposed by careless and/or dishonest retail people in face-to-face transactions (this, BTW, is the only type of fraud anyone has every tried on me, and I caught it in Quicken only a day after it happened).[/li][/ul]