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.  
 
Please note that ClamWin Free Antivirus does not include an on-access real-time scanner. You need to manually scan a file in order to detect a virus or spyware.  
ClamWin Free Antivirus is based on Clam AntiVirus engine and uses GNU General Public License by the Free Software Foundation, and is free (as in freedom) software.