I use an old 64 bit OS
A little known fact and one that I think is deliberately kept a secret is that there are no known viruses, trojans or root kits for 64 bit OS's.
At one time a 64 bit virus was made just to prove it could be done, but never released. 64 bit OS's are much more secure than 32 bit.
With 64 bit OS's becoming more common, I'm sure that will change, but the info is no more than 6 months old.
Somewhere I read a good analogy for the way people use their comps.
If you want to walk across the street or drive somewhere, you use reasonable thought processes to accomplish this. You look both ways before crossing to make sure it's safe. Stop for red lights and stay out of areas that may be dangrous, etc. Simple common sence things to stay safe.
People get on their comp and act completely different, just the opposite. They armor up their comp with all the anti virus, spyware and any other software they can find to try and stay safe. Then they blindly blast full throttle into the darkest depths of the internet hoping they wont get hit, yet they always do.
Smart computing and common sence is the best security. The only security I use is the Comodo Firewall that will stop anything from running on my comp unless I allow it.
If I have a file I think may be a problem, I use an online AV to scan it like Virus Total -
Click Here.