I'd like to expand on what Keef said. The primary safety system here is "the pilot": i.,e. you, the user. Try to avoid trouble in the first place. You're not daft and many of you are actually licensed to navigate large metal objects at high speed over densely populated areas: so why is it so difficult to avoid clicking the mouse on a "don't do this" button?
Anti-virus software is there to help you when something is already going wrong. You should no more rely on Norton etc. to prevent infection than you rely on TCAS to prevent collisions.
It is unfortunate that the marketeers will try and sell you "100% safe internet surfing" or some similarly bovine ordure, but that's about as realistic as a 100% safe aeroplane.
On the other hand, do continue to open attachments and download software without thinking too much about where it's come from: it helps people like me pay the bills, when we come round and clean up the mess.