Open Source Virus Scanner

[Falcon21]

Check out this website: http://www.clamwin.com

ClamWin Antivirus is an Open Source (free) Virus Scanner Toolkit for Microsoft Windows NT/98/Me/2000/XP/2003. It provides User Interface to Clam AntiVirus scanning engine.
ClamWin Antivirus Features include:

* Scanning Scheduler;
* Automatic Virus Database Updates. ClamAV team updates Virus Databases on a regular basis and almost immediately after a new virus/variant is out;
* Standalone Virus Scanner;
* Context Menu Integration to Microsoft Windows Explorer;
* Addin to Microsoft Outlook.

[Spyder32]

I like OutPost better. Added skins and whatnot, you could easily add. Either way though, an OpenSource virus scanner is the way to go.