if i may add to the linux security answer. virus's are mostly made for windows computers as windows is the more popular OS so more people will be effected. My mother can install linux but i wouldnt trust her to set up a secure webserver for example because she has no idea what she is doing.
The Ubuntu community is made up largely of linux newcomers and im pretty sure that thay are equally clueless about security. if they have the choice of which ports to open for an application do you expect everyone to really understand. no of course not.
the security problems that people have are, like always, user errors. red hat enterprise give you paid support from linux experts so you can be more certain of their ability than my mothers.
and as for no problemo mac users, the "it just works" BS, the take it out of the box, plug it in, and away you go attitude, why do they have a huge support website??? WHY~!
anyway..