Virus scanner is a necessity in the Wintel environment.
My Thinkpad X40 came w/ Norton Antivirus 2004, but last week it told me that it would expire in April and asked me to renew my subscription. You stingy git! AVG (which the Lady’s computer is running) and Avast! both have free offerings and are arguably better, and certainly more aggressive in updating their virus signature database.
I installed Avast! 4 then uninstalled Norton (should have done it the other way around, but no big harm done). The initial impression of Avast! is excellent. Many advanced features, such as monitoring IMAP, SMTP and HTTP network activities, which I might switch off eventually, but I do like the rolling ball icon.