Sorry, you are wrong. That is simply not true. Yes, any platform is susceptible to Trojan malware. However, OS X has built in protection against all known Trojans. . . and there are only 57 known trojans for the OS X Mac platform. Compare that to the number of trojans known for the Windows platform. . . and that alone shows the failing of your assertion.
It takes industrial strength stupid to continue such behavioral activity to install such malware, which ALSO requires the input of an Administrator's user name and password, not just the click on an "OK" check box warning to override protection. It takes an affirmative knowledgeable action.
Most writers of malware target the low-hanging fruit. That means they write their malicious wares for the Windows platform.
However, there are no known vectors for other types of malware such as words or viruses to get into OS X UNIX platforms at this time. There have been seven (7) virus/worm candidates offered for such malware in the past twelve years and all of them have failed for lack of viable vectors to invade the machines. That leaves ONLY Social Engineering as a means of malware invasion or physical possession/access to the computer. Windows machines are still being attacked via other means.
OS X has built in protection against all known Trojans. . . and there are only 57 known trojans for the OS X Mac platform
And...
That leaves ONLY Social Engineering as a means of malware invasion or physical possession/access to the computer
You made my point for me. I said they are a TARGET for MALICIOUS content. I said nothing about viruses or specifically about Trojans. I said that they are susceptible if properly executed. I said nothing about the difficulty of infection, simply that they can be infected, so the assertion that Macs are immune to viruses and malware is patently false.