It has become popular belief now that the Mac platform is becoming flooded with malware. Most of this belief is coming from the Antivirus software companies trying to sell Mac antivirus software. In fact almost all of the Malware for Macs is proof-of-concept and very few of these are actually found in the wild. What malware is spreading for Macs is mostly on P2P File Sharing networks and Pornography websites. Under normal use, it its still very rare to encounter any type of Mac malware and the main use for Mac Antivirus software is still just to detect Windows Viruses so that you do not accidentally spread it to a windows using friend by email or Flash media.
This is not to say that Macs are totally secure, far from it in fact. Apple releases regular security patches just like Microsoft does for windows and it is very important that they be applied. In Leopard and Snow Leopard updates are downloaded automatically and you are prompted when to apply them. In Tiger you must configure the update interval in System Preferences or check manually. Older releases of Mac OS are no longer supported.
