|Ok, point taken - so I'll try: |
In short, given the conditions you stated in the last para of your original post if you just leave the computer on with no browser running it is unlikely to be infected, even without an AV.
It all changes when you go online and start browsing around. That is why I would agree with others that an AV is worth having, both now and particularly in the future with no further security updates. You can get AV's free which are quite good enough and are not intrusive.
Remember that the virus/trojan/rootkit writers have become far more sophisticated since 2005.
Hope that answers your question.
Always pop back and let us know the outcome - thanks