David,
For what it's worth, my thoughts:
1)Avira commercial packet (not that expensive) is about as good as it gets for protection.
2)Spybot is very memory intensive, if you have the RAM for it, however, it can stop many worms before their signatures are recognized, their heuristics are good. Just, if you're running XP, go up to at least 2G, if Vista go for the maxium 4G, Windows 7 you should be ok with 2G but 4G won't hurt. Yes, Windows 7 is less memory intensive than Vista was.
3)CCleaner is very good at finding icky stuff in the registry you'd never expect and fixing it without damaging anything. Always take the program up on the offer to make a backup first, only takes a few seconds.
Now, McAffe has some very good virus clean-up tools, their regular anti-virals don't however, test better than Avira and you have to invest some time in learning how to work with it. My dad swears by it.
Here's some general hygiene steps which will always help:
1)Print a copy of Jeff's post above and put it on each desk, next to the keyboard. Good advice.
2)Are your firewalls working? Windows gets better from month to month, but a really good firmware firewall built into a router is still your first line of defense.
3)Does every single computer in your office simply have to go online/access email? Could you set things up so that only one computer accesses the internet/email and then, after virus checks, the others get the files? Any modern server or even dedicated router can set up such a topography.
4)Worms are notoriously hard to lose. You probably have the source code for them in archived files. You're either going to have to be consequent or keep getting re-infected.
5)Operating Systems.
Here are the advantages/disadvantages of the three most common OS:
a)Windows
Advantages: Compatible to everything, just works.
Disadvantages: Most targeted OS for viruses and worms, hardest to protect because NT was not designed by a paranoid schizo, but by a love-in, trusting beatnik.
b)MacOS
Advantages: Relatively safe. Plays well with other systems. Easy to learn, easy to set up. Beautiful design
Disadvantages: There have been several successful attacks on the system over the last few months as enough hackers have figured out the few weak spots and take enormous pleasure in pricking the "we are immune" mentality of the MacOS community.
Very, enormously, expensive relative to Windows or Linux. As a monopoly, Apple can and will tell you when you must buy new hardware and software and they do actually just go in and turn off software at will on user's devices when it suits them.
If you can afford to replace your entire system every few years and your staff aren't in a position to learn Windows security or Linux OS, MacOS is a very, very good choice. You are, however, at the beck and call of Apple and they determine what you may buy and when you must buy it.
C)Linux (Ubuntu, for instance)
Advantages: Safe as MacOS, cheap (you'll pay for support, worth it), flexible, easy to customize to your needs. Runs on Windows machines with no problems, at all. Ever.
Stabil, fast, plays well with others, supports older and newest hardware and software, hard to break and easy to fix.
Disadvantage: Really tough learning curve. Of all the Unix group, the hardest to learn. Only disadvantage.*
If you have money to burn, go with MacOS. If you have no money but need security and can afford the training time, go with linux. Otherwise, follow Jeff's advice and my one or two suggestions and it will get better. I backup regularly, by the way...as in, every night at 3.00a.m.
*I don't understand why the Linux community hasn't tried harder to make their user interface as friendly and easy to learn as MacOS is. (AT&T UNIX begat BSD, BSD begat MacOS X, no I did not say MacOS was Linux, but let's not pretend it sprang from Steve Job's head fully formed, either...it's Unix made pretty.)