Okay, man. OS X is inpenetrable. Whatever you say.
I didn't say it is impenetrable, I said it is very, very difficult to do. It is not a trivial matter.
One UNIX security expert has said "No OS is impenetrable but where the effort to write a virus on a Windows box is a 1 on a scale of 1 to 10, the OS X Mac is a 9."
Trojan horses are always possible... psychological persuasion to do something stupid can work whether you are running a Mac or a Windows or a Linux box... but even with a Trojan, on a Mac, the damage is limited to the permissions the user has.
Noone in the Mac community is suggesting that OS X is inpenetrable or that Mac users should not use best practices. We're simply saying that Mac OS X has a proven track record of being demonstrably safer than Windows, thanks to better software engineering. The Microsoft stooges who claim that the Mac's excellent safety record is attributable entirely to market share are wrong. If Mac OS X had the same shoddy design as Windows, we'd have a plague of virus infections too.