Call this "tough love", the way to deal with malicious files at whatever level is to let them come in and that way you can know how to remove them. You can download software and plugins. That will not deal with the files, but hopefully avoid them. What happens is when Norton or another well known service finds new viruses online, they make upgrades to their programs. This is why you will never have a complete anti-virus program, because the virus programmers out there are busy making a new one that can get around the latest prevention methods (anti virus program, ad-blockers, email scanning, etc...)

If you can't stop the viruses from coming in, and you are scared at the notion of letting them in, please consider getting a "HIPS" program, http://en.wikipedia.org/wiki/Intrusion-prevention_system

http://www.techsupportalert.com/security_HIPS.htm (I have used Cyberhawk, second one listed, and now that I found this link I think I'll check out a few others)

A firewall I use and like is Comodo Personal Firewall http://www.personalfirewall.comodo.com/

When I had my experience with a virus earlier this year, both Comodo and another firewall I was testing immediately alerted me when the main files of the virus were re-installed and starting to execute them. So it gives you plenty of time to reboot in safe-mode and deal with them. Obviously, if you have an older virus hit you, and you have an anti-virus program, it will not only do the same but remove them for you (sometimes with a reboot necessary). With the HIPS program, it goes a few steps further and learns your behavior to determine intrusions.