Need anti-virus software? Ward Stanke sends us some very useful information. Read on: Snow Leopard and Lion contain a malware blocker! Here's an article from Macworld. This malware blocker has been very quietly, but consistently, updated by Apple to handle the most dangerous, and the most recent, malware threats.
See this: Mac Malware "Explosion" Missing In Action.
Here's an excellent up-to-date web site about Macintosh malware....and an associated Macintosh Malware Catalog that rates the individual threat posed by each piece of malware. Note that most of the threats listed were either rendered moot by an Apple update, or they never really worked, or they were never seen in the wild or in significant numbers.
Mac OS X anti-virus software: More trouble than it's worth? Here's a review.
This is an article simply entitled "Wolf." It is about the press crying "wolf" for the past 7 years with regard to the "coming wave of Mac malware": Daring Fireball: Wolf!