Im sure its on purpose.... *rolling eyes* at mac fanatics.
Nobody is perfect and its asinine to believe the exploits are intentional.
In any complex system there are bound to be ways to exploit the system, against the good intentions of the authors.
The skill level required to crack Windows is much lower than the skill level required to crack Mac OS X, and admittedly - Windows has become more difficult to crack than it was only a few years ago.
The weaknesses in Windows that make network viruses possible is due to features in the software that use those exact same weaknesses for legitimate purposes.
On a Mac some of these weaknesses exist, for exactly the same reason they exist under Windows, because they're useful for legitimate software. The primary difference between Windows and the Macintosh is that it is more difficult to exploit those weaknesses to run malicious code, or to replicate and spread a virus.
You don't have to accept this fact because it is difficult to prove in the absence of email/network viruses for the Macintosh, and the absence can't be accepted as proof.
It has nothing to do with fanaticism that people like me defend the Macintosh. We're just pointing out that the Mac is inherently secure, separate from the security obtained by its so-called obscurity.
So, if and when, the system crackers start going after the Macintosh, it will take their elite and most creative minds to succeed. The amateurs and less brilliant script bunnies that are hopping around the internet attacking Windows machines just don't have what it takes to create a self-replicating, propagating virus for a Macintosh.