I use an iBook usually, OS 10.6 and the Safari browser. By the way, David uses a Mac too. I haven't had any virus problems or anything else of that sort and have read on reliable sites that there are no OS X virii in the wild. At least one has been written but it was not released.

Apple releases security upgrades occasionally and I always download them right away. I also have Virex because it is included in the .Mac package I subscribe to for use as a backup site. I've scanned with it a few times but it has not turned up anything.

Use the Software Upgrade function regularly and use the Safari browser and you should be fine. On other message boards, I often see flurries of messages about spyware and such but I'm never affected. It's not cost effective to write malicious code for OS X as it just doesn't have the gaping security holes that are intrinsic in Windows and Explorer plus the market share is small.