If you’re running Windows and you are connected to the internet and you aren’t taking security precautions then your PC could easily be one of the 30,000 PCs that are hijacked every day for the purposes of spreading viruses and sending spam.
Microsoft has a page of advice on how to cut down the danger. I’d basically say that you need to do three things:
1/ Install and use a firewall.
2/ Use Firefox instead of Internet Explorer for viewing web sites.
3/ Use Thundebird instead of Outlook for reading email.
If you’re not taking basic security precautions then, in my opinion, you shouldn’t be allowed to connect to the internet. It’s like being allowed on the road in a car without a license. Except you don’t annoy quite so many people in a car.
Update: Four things (cue Spanish Inquisition sketch) – I forgot about installing (and keeping up to date) an anti-virus system.
p.s. Look, I wrote this whole entry without suggesting that people should just stop using Windows and switch to Linux instead
I wrote the following for people at work, and I’ve pimped the link to others from time to time:http://sparky.ox.compsoc.net/~grimoire/winsecurity.html