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Macs
It's not hard. They've got just as many flaws as windows (google "mac hacked" and look at the comments of the attacker).
It's just…
No one cared enough about them to look for holes.
Now people are… And since it's based on FreeBSD (from what I know, correct me if I'm wrong), even more hackers know how to work with it, and how to mess it up.
There are many texts on attacking Macs running OS X. Check out the security focus mailing lists, there was a thread about this just the other day.
As far as your request on how to hack them goes, like any other hack, it depends on the situation. There is no one method to use. Take into account the situation, and then act accordingly.