I recently installed two pieces of software that will help defend my computer against viruses and other harmful programs. You can do the same for free. Here are the links. These are the best free tools as of May 2008.
Apparently this is the new favorite free firewall tool that is replacing Zone Alarm in popularity.
Avast! Home Edition - Anti-Virus protection
I hate using anti-virus software because it always seems to bloat my computer while offering minimal protection. I've tried Norton, and Windows Live One care. Both of them work reasonably well, but when the subscription runs out, I really hate paying for a new one. So this free version is a welcome addition to my computer. When I was reading up on Lifehacker about the reasons people don't use anti-virus software, Avast was the only software mentioned that people liked having on their computer.