Yesterday's Washington Post Security Fix disclosed that on November 21st of this year Apple put out a technical note where they recommend the widespread use of anti-virus software for Macs, including specific recommendations for Mac AV utilities.
I've never believed the "Macs cannot get a virus" mantra that some people spread. The reality is that any computer where the user has the ability to write to the hard drive or install applications is subject to a program doing evil deeds without their knowledge.
I've been a Mac user for 10 months now—a relative neophyte—but have learned a couple of things that have carried over from my Windows days. The single most important one is to be very careful about which software I allow to get installed on my Mac. When I install something that comes from the web I get a little confirmation dialog:
In addition when I try to run full installation programs I will often get prompted to enter the administrative password for my Mac:
Some applications, like those based on Adobe AIR's development platform include their own warning dialog:
In all of these cases it's critical to stop and think about what you are doing. This is a virtual knock on your door where you get a chance to either turn someone away or let them in your home. It's critical that you take a moment and think about what you are doing; don't just blindly enter your password or allow software to be installed. If you have gotten into the habit of blowing past these dialogs then you need to stop doing that and think it through.
The other thing is to stay current with Software Update. When that little globe is bouncing on my Dock Bar I generally install the updates that it recommends.
Do you run anti-virus software on your Mac? Though I'm very cautious with my own machines I do worry that my wife and teenage children will not be as diligent.