Especially their operating system.
Look how big the anti-virus market is....
Amd that problem is exclusively Microsoft's....
Heard of "Black Hat Conventions"?
This is where the best hackers are invited to come in hack products to help developers find holes. Of the 3 products Microsoft, Linux and Apple, Apple is the first to get hacked. Why? Because hackers are not focusing on something with such little desktop marketshare.
Within the Smart Phone space, I'm sure you've heard of more Apple problems as Microsoft has a much smaller share.
As far as Virii are concerned, that has more to do with stupid users who are too dumb to keep their systems up to date and fall for stupid stuff on the Internet. These are the same idiots who run their systems with Administrative level access so if something happens to their system, its a disaster.
I work in IT, that's how it is.