/enemy wall of text spotted
firewalls effectively stop 99.9% of all internet-borne worms and threats (including your ISPs firewalls at their own router level.) most network based threats use exploits in well known protocols to spread, and most firewalls block these protocols (as well as actively protecting against unusual behavior in the event a port is successfully compromised.) it is somewhat riskier on a corporate network since most client computers are a bit more 'open' on the network, but even these threats can be successfully mitigated if you have a modicum of knowledge of network security and access controls.
this leaves user-error as the number one threat to your network and computer. the ones who click on pop-ups and install spyware, visit web sites that exploit code vulnerabilities and the like... these people can be contained as long as they don't have admin level access to their systems, but most places still allow at least the primary user of the computer local admin rights, hence the spyware and virus infections on some people's machines. even these isolated incidents can be contained fairly easily, with the majority of inconvenience to the user who infected themselves in the first place.
being scared of the internet is not necessary... skepticism is fine, but paranoia is often unfounded. if you understand how viruses and security exploits work then you know that AV software is only acting as a safety net for mistakes you shouldn't be making. now there is still that .01% chance of getting a root-kit, or random bad cookie, but if it can slip through multiple firewalls as well as your safe-surfing habits, then no two-bit, piece-of-shit, anti-virus program is going to do anything to stop it. i would rather use my resources for gaming instead of allowing some 'real-time' scanning junk to clog up my shit. ya know, AV programs are, by their own definition, a virus in the way they operate. to "protect" your computer they have to hook processes and intercept calls to the cpu. viruses do the same shit, although with different goals. i'd rather not have any of it on my system, viruses or antis.
funny story, a friend of mine who also works on a school network was telling me the last network virus threat they had was spreading through the open port symantec was using for liveupdate. if a person didn't have AV on their computer, they didn't get the virus. ironic?
