I’ve been using ClamWin, an open-source and free antivirus program for about two years now. Its is absolutely the best open source product I’ve ever used (next to Mozilla Firefox). When my original Norton Antivirus expired and they wanted me to pay in excess of US$50 to renew, I decided to look elsewhere. And to me, this product, ClamWin, proves the open source model works, and the quality of the products either match or exceed their counterparts. So I highly recommend this software which integrates with Microsoft Outlook, and runs on WindowsXP like a bomb! Download ClamWin 0.88.5 here.