Sorry to burst your bubble...but Linux is not immune to virii of any type, or any other kind of attack that plagues Win machines.
At the moment, most of the installed base of desktop PC's and a good portion (not sure of the percentages, but I would guess at least 40%) of the servers run Windows. SO most of the attacks are tossed at win boxes.
(Yes, some of the lousy default settings for security dont help)
But there have been plenty of exploits (relative, naturally) that effect Linux./Unix. (I remember a couple mail exploits that gave root access some years back, as well as the more recent slapper.)
Trust me. Virus writers will turn their heads towards Linux and find a good target when they do...because unfortunately many Linux people have decided that "security is great on linux" out of the box and think they are completely safe because of permissions, etc.
While an out of the box (or off the ISO) install of Linux might be more secure than a Win box freshly installed before tightening up occurs, it certainly isnt completely secure.
Viruses and hacks aren't a "Bad OS" or "Evil software company" problem.
They are a "Dishonest person who spends every day all day long looking to find something to exploit or to make a new exploit in some fashion".