About a week ago, I had a conversation with some of my friends regarding the bullet-proof operating systems. One of them informed us that one of the Government organization decided to replace Windows-based workstation and to use Steve Jobs' MACs because they like UNIX kernel are not penetrainable due to the security architecture and required permissions from the kernel to use any external program. While I agreed on the kernel itself, I disagreed that MAC is a bullet-proof OS. The problem with any OS that it's not only kernel itself but the whole bunch of other files that participate in various services, supporting applications, and much more.
I liked MAC for a sleek interface and performance but not for the price tag. Also, Vista offers the same grade of a quility screen images and comparable performance. To support my statement, I sent them the link to the following article where the number of security problem were addressed:
"If you look at the number of found vulnerabilities in Windows XP (28) vs. Vista (11) this year, Vista wins again. If that seems like a lot, don't forget Mac OS X has had 101 in the same time period".
No matter what the OS is being used and level of the security applied, the weakest link is always the end-user.