If you’re running on a Macintosh, you really don’t need anti-virus protection…unless you’re running Windows on your Mac. If you’re using Parallels, VMWare, Bootcamp, etc. you’ll want to install anti-virus/spyware protection on the Windows partition of your Mac. (To protect against other potential internet security threats see this article and use OpenDNS.)
It’s a reality in the Microsoft Windows world that you definately need to protect your computer from viruses, spyware, and malware. We’ve seen some utilities like Norton Antivirus from Symantec to be truly invasive and cause problems. They 
slow down your computer and ask you tons of questions all the time. So here are the three applications we recommend that will provide reliable and fast protection:
1. SuperAntiSpyware. It’s exceptionally affordable at only $19.99 for a LIFETIME subscription for TWO computers. Contact us if you’re interested in multi-user or site-wide licenses.
2. Malwarebytes. For about $25, get an excellent protection app for your Windows PC.
3. Microsoft Security Essentials. Free security from Microsoft that is simple to install and easy to use. They call it the Anti-annoying, anti-expensive, anti-virus program.
Before installing these protection applications, be sure to completely remove all other anti-virus utilities you may have including Norton Anti-Virus.
[...] Windows anti-virus/spyware utilities that are thorough, reliable, and [...]