And those users that have installed the SP blocker built by Microsoft to get around all the problems associated with SP3.
If you browse the internet of open email without having security updates and without having a virus scanner, you should probably be doing something else with your time.
There is another free and relatively painless preventive, which I use with my business clients.
I do occasional backups of System State. It takes about two minutes and can be scheduled.
Restoring System State after a virus attack takes about ten minutes — including a reboot and reinstallation of updates.
I recovered four machines by this procedure. It’s a lot less painful than tracking down spyware removers, and a lot faster than reformatting. Unfortunately I need tricks like this, because the companies I work with do not restrict internet access, and given enough users, some will install almost anything.