Not protected by antivirus software? With both free and commercial solutions available, there is little reason not to protect yourself.
A nice, free solution is Clamwin. You can even run it on a USB thumbdrive by downloading it from PortableApps.com.
Not sure about using freeware to protect your computer? For commercial solutions, there is nothing better than Norton Anti Virus 2007. Norton will protect your computer from Viruses, Spyware, Trojans and Worms. It automatically detects and removes Viruses, rids your computer of unwanted Spyware, and scans Email and Instant Messaging attachments for Virus threats. Learn more about Norton on this site.
Whether you choose a free or a commercial solution, remember to practice safe computing!