I like the AVG antivirus package. Much more trim memory footprint than McAcfee or Norton and doesn't bring your computer to a crawl when it's scanning. Virus def. updates occur quicker too when something comes out. Then for spyware, I've got the Lavasoft Ad-Aware and Spybot Search & Destroy.
I used Norton for years, but never any more. Last year an upgrade to the 05 version crashed my OS. Foolishly I fresh installed the 05 version. Recently I upgraded and purchased two backup hard drives which can be swapped in and out in case of a virus or system crash. Norton cancelled my subscription before it ran out. They say I loaded the software more than three times on too many hard drives. Well of course, that's what backup is all about. Symantec apparently didn't or couldn't bother to check that the software was only used on only one motherboard. I am not happy about this experience with Norton, but they undoubtedly did me a favor.
It is true that most virus scanners dont pick up alot of viruses. Some viruses even target at shutting down the firewall and anti-virus applications. Since you mentioned you are a business, I would strongly suggest Symantec Corporate Edition. They are fairly cheap to license and offer *good enough* protection and support. It also uses very little system resources, which can be the downfall of other scanners. If you are getting viruses through email, there are a few things you can do to stop them from infecting you. 1. dont open attachments that look fishy or from people you dont know. 2. make sure your email program is not set to open, by default, attachments in emails without your specific permission. 3. block the addresses where the viruses are coming from. 4. block certain file extensions all together. such as: .exe, .zip - Most of these options can be found in your email client. I would strongly recommend scanning your hard drive from time to time with programs such as Webroot's Spy Sweeper, A2 Free, Spybot in addition to your virus scanner. I wouldnt allow them to run in the background because they can heavily conflict with whatever virus scanner you have installed. Your best bet for protection from worms and viruses that spread through from other computers on the Internet, is a seperate, network attached firewall. (if it will work with your setup)(some routers have similiar features built in). These devices will stop most attacks that can come through your network or the Internet. They are also easy to install and use. Some links: http://www.webroot.com/consumer/products/spysweeper/ http://www.emsisoft.com/en/software/free/ http://www.symantec.com/Products/enterprise?c=prodinfo&refId=805 http://www.safer-networking.org/en/download/index.html http://www.newegg.com/Product/Product.asp?Item=N82E16833181102 http://www.newegg.com/Product/Product.asp?Item=N82E16833122007