And for a solid, reliable for-fee product, I recommend Symantec Norton Antivirus 2006
"Symantec has ...over 20,000 sensors monitoring network activity in over 180 countries. Symantec also gathers malicious code data along with spyware and adware reports from over 120 million client, server, and gateway systems that have deployed Symantec's antivirus products. In addition, Symantec maintains one of the world's most comprehensive databases of security vulnerabilities, covering over 11,000 vulnerabilities affecting more than 20,000 technologies from over 2,000 vendors. Furthermore, Symantec operates BugTraq, one of the most popular forums for the disclosure and discussion of vulnerabilities on the Internet ... The Symantec Internet Security Threat Report is grounded principally on the expert analysis of this data. Based on Symantec's expertise and experience, this analysis yields a highly informed commentary on current Internet threat activity...."