Ive run PC's on the internet since the old 8088 machines were around. Before that I ran an atari 800 xl on the old backbone system (remember FIDO net?)
In all the years and all the machines. I never had a virus. Why? Because I never ran Internet explorer and never ran outlook or outlook express. Plus I ran my network without virus protection for several years as well. I never once felt insecure about the LAN network.
How?
First, every thing is behind a router which stealths the entire LAN from the internet. A good router closes all but the very necessary of those 64,000 ports your machines has.
Second, I run a two way firewall. Presently I still use the FREE sygate firewall even though it is no longer available. Good firewalls will detect a change in your software and alert you if something is amiss. You must use a two way firewall for complete safetly. Microsoft firewall within XP is not two way. It does not prevent maleware from signaling out. You may be surprised to see how much outgoing traffic your machine is doing. Almost every software you use signals out to some central server. (remember the loveletter virus)
Almost all malewares came into your machine via Outlook or Outlook express while set in the preview mode. They would attack your machine and use your mailing list to spread to your friends. (remember KLEZ & Chernobyl, & Melissa virus?)
So, for all those who use those all in one suit packages that claim to protect everything. You simply do not need all that if you avoid the targeted M$ products. Period.... Also remember that Norton and Mcafee became very popular because they used a service to market thier goodies with magazine column authors. Lesser known products refused to participate in these schemes.
Firefox and Firebird? It was the darling of the guru's while it was still in pre-beta. It cannot be attacked because it does not contain the exploits that plague M$ products. No popup exploits, no back doors, and no fancy bells and whistle code.
So, those MAC guru's may dream on who try to claim that MAC hardware is better. It is not the machine that brings the infections. Its the software used within. Those who were dependant on M$ products suffered. Those who listened to genuine computer geeks (and not the bedroom self professed mechanic) used other market products lived on without pain.
For those who must have every single M$ update in order to feel clean and tidy. 99.999% of those exploits you hear about have nothing to do with you and will never affect you. There is an entire industry who claim money for every possible micro crack they can find in windows code.
Case in point. All the machines in my place have not updated anything M$ in years. The very last update was SP1. after that nada, nutin, no way, no how.