ClamWin is an open source, free version of anti-virus software (think Norton, McAfee). You should have some virus protection on your computer. ClamWin offers at least some protection, so if you don't have anything it's certainly an option. While ClamWin can scan your computer and individual files for viruses and spyware, one feature it does not currently include an real-time scanner. In other words "you need to manually scan a file in order to detect a virus or spyware."
From the Site:
Download Clam Win Free Antivirus"ClamWin is a Free Antivirus program for Microsoft Windows 98/Me/2000/XP and 2003. ClamWin Free Antivirus comes with an easy installer and open source code. You may download and use it absolutely free of charge. It features:
* High detection rates for viruses and spyware;
* Scanning Scheduler;
* Automatic downloads of regularly updated Virus Database.
* Standalone virus scanner and right-click menu integration to Microsoft Windows Explorer;
* Addin to Microsoft Outlook to remove virus-infected attachments automatically."