I recommend Nod32 and Symantec Corporate (NOT Norton) and AVG as the best Anti Viruses on the market. I know from experience with dealing with viruses and spyware and everything else on both sides of the fence what works for me. I admit I haven't tried that many Anti Virus programs but out of the ones I have tried and talked about with Security minded friends and associates they agree with me that those are the two best on the market. I recommend to try these even if you already think you have a good antivirus you won't really know how good it is until you encounter something really shitty or some "undetectable malicious code". Be careful out there and use good programs and your brain and you should have no problems with virii.
1) install NOD32 Business Edition
2) apply any of the keys located in the archive
3) install the fix and THEN restart your computer
Update the virus definitions and that's it. You're set utill January 2050. Tested and working on WindowsXP/Vista