there are no trojans for Macs yet.
i know of 7 different viruses for Mac, as opposed to about 600+ for PC.
the more people that use Mac, the more viruses will start being created. but, in all fairness, the targets most hackers and attackers choose are big businesses, high-ranking people, government systems, etc. it is extremely unlikely that most of those targets will ever switch to Mac, therefore most Mac users don't have much to worry about. Mac users don't matter, therefore the community doesn't care about them.