Also notice the exploit requires, as Bill pointed out, that you download and install pirated software -- that's not an indication of a basic flaw in the OS X architecture
The difference between a flight sim program on a disk, and a "virus" or "trojan" on a disk (or download) is just the intent of the program -- from the computers perspective they're just bits and bytes. The computer does what the program instructs.
The trick from a hackers perspective is getting the program onto a victim's computer. The method above requires intervention -- and a monumental level of stupidity -- by the end user. Pretty ineffective when trying to build a network of infected machines (a robot network, or "botnet").
I'd also say, that from a "networking" perspective, if someone asserts that OS X and Linux have a limited support network they should take another look at the Linux developers forums, or at Apple's record of timely security patches.
For those who can get to a terminal window in OS X you'll see an operating system that looks remarkably like BSD Unix (because that's what its based on). Unix operating system architectures inherently partition privileges and "sandbox" processes so it is much more difficult for a compromise to take over a computer. This is the model that Microsoft is moving towards with Vista and Windows 7. Of course Unix has about a 35 year head start. On the Linux Ubuntu 8.10 system I'm on right now I run at a reduced privilege level as a regular user. I could bypass that but it would be more trouble that its worth, and I gain nothing as far as system usefulness or function. Linux and I manually elevate privileges when I need to do system maintenance.
Hence the need for end-user intervention to infect a system like OS X. Not a great way to build a 1,000,000 node "botnet" (if there are that many Macs on the planet... (sorry Bill

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With so many "easy" Windows systems available throughout the world what would be the point of developing a virus or compromise for OS X or Linux? With OS X and Linux nominally more difficult to get into in the first place, and providing a smaller base of systems for building a botnet, developing malicious code for either is kind of a waste of time. I guess you could do it to prove you could do it ...or, that you like to FAIL!
