Once again...security by obscurity is no security. Reason they don't exist is because there's not enough bang for the buck for the hackers. Oh and btw, they do exist...ever heard of Leap-A or Oompa-A. Now what's your defense.
Previous versions of Mac OS had lots of viruses in the wild, and they had nowhere near the market penetration or visibility of OS X, which has none.
Oh and btw, they do exist...ever heard of Leap-A or Oompa-A. Now what's your defense.
Leap-A/Oompa-A was a trojan, requiring the person to purposely run it and be running as administrator (which is not as common in the Mac world due to the better permissions set up in UNIX). I believe the first malware for OS X was a supposed pirated copy of MS Office, which if ran deleted files in the user's profile (but couldn't hose the system due to lack of root permission). There was one reported case of getting nailed by the latter, none that I heard of with the former.
Leap-A or Oompa-A, actually the same "virus" under different names, never existed outside of a laboratory proof-of-concept created to try and gin up interest in Mac AV software.. It was never in the wild. Intended to spread by using iChat, it took TWO Mac software engineers from Macworld and TWO computer security specialists from Secunia (one of the security agencies that reported it) working SIX hours to get the virus to spread from one Mac to another Mac... and then it didn't work as advertised. When they DID get it to the second Mac, it required that Mac's administrator's permission to install and then again to run for the first time. Some threat.
Inqtana-A, another claimed Mac OS-X "virus", was actually created by one of the guys running the Month of Apple Bugs... and if failed for the same reason. It also was never seen in the wild and was a mere proof-of-concept that fell flat on its face and was laughed out of the Mac user's world of worry. Inqtana was designed to spread from one Mac to another by way of Bluetooth... but the target had to accept the malicious file from someone literally within 30 feet of the target computer, download it, click OK on the warning that the file contained an application, provide permission to install it and then again to run it. Whoop-do-doo. I am so threatened.