But I'm perfectly happy with XP's level of security. 

I don't even use anti-virus software.  More trouble than it's worth, IME.  I've been online for 15 years now, and never had problems with malware.  I don't use Outlook or Internet Explorer. I do use a firewall...and basic common sense when it comes to e-mail attachments and the like. 

It  would be different if I had kids using the computer, or even my parents, who can be a bit clueless.  But it's just me.