I have written several times about free anti-virus programs for Windows. If you are using a Windows computer, don't even think about using it without an anti-virus, anti-spyware, anti-rootkit, and anti-Trojan program installed, along with the latest updates for that program!
In the October 1, 2009 newsletter, I described a brand-new free anti-virus program that had just been released by Microsoft. When describing Microsoft Security Essentials (MSE), I wrote, "I don't have a virus testing lab so I cannot vouch for its performance." Now someone else with a virus testing laboratory has tested it and gave Microsoft Security Essentials a top rating for malware removal as well as their best ranking in a performance test as well.
AV-Comparatives.org ran a series of real-world tests running through common scenarios such as downloading, extracting, copying, and encoding files, installing and launching applications, and they also ran through an automated testing suite as well. Three different products passed all the tests with flying colors but Microsoft Security Essentials was the only one of the three that was also very light on system resources.
You can download the free Microsoft Security Essentials at:
Windows XP 32-bit (8.61MB) at http://download.microsoft.com/download/A/3/8/A38FFBF2-1122-48B4-AF60-E44F6DC28BD8/mssefullinstall-x86fre-en-us-xp.exe
Windows Vista/7 32-bit (4.28MB) at http://download.microsoft.com/download/A/3/8/A38FFBF2-1122-48B4-AF60-E44F6DC28BD8/mssefullinstall-x86fre-en-us-vista-win7.exe
Windows Vista/7 64-bit (4.71MB) at http://download.microsoft.com/download/A/3/8/A38FFBF2-1122-48B4-AF60-E44F6DC28BD8/mssefullinstall-amd64fre-en-us-vista-win7.exe