Security: There's passive, reactive, and proactive.
Reactive: Wait until there's a problem and then 'fix it' with a tool or some
antivirus program. Problem is, it will reoccur unless you become Proactive.
I'm running Ewido and NAV
Proactive: Bar the gates and repell all boarders! The FIREWALL keeps the little
buggers out (unless of course you invite them by opening any/all attachments).
The cheap and easy way is to just enable the Windows Firewall. Almost any
other is a BETTER choice

I run Norton NIS and it is effective.
Also run Spybot S&D, and Spywareblaster to control ActiveX
Passive: This is a setup and forget solution that is a major assistence.
It's called a ROUTER with NAT(Network Address Translation). This will act
very much like a firewall, in that it is not easy to cross from the public WAN
to the private LAN space.