Close, the first rootkit was written for Unix, which has been around longer than Windows.

While there is truth in the statement that any system can be hacked, and Windows is more popular as a target because it is a bigger target, the main problem has been that the system is more open to "automated" attacks. The infamous "script kiddie" some pathetic loser whose life is so pathetic he has to cause trouble by using tools written by others. A fairly massive weak spot is Microsoft's attempt to maintain backwards compatibility, this has led to flaws coming back many times when they thought they had sorted the problem. You could make an argument that tying the browser to the operating system at such a deep level, as they did with Internet Explorer, was the single biggest security gaff ever. A computer running Linux can usually be hacked, but for the most part, it is necessary to target the actual box in question, and find out what openings have been left unpatched. Some systems are harder than others, OpenBSD for example, or one hardened by the application of SELinux mods ( Stands for Security Enhanced, originally written by the NSA )

My analogy is that running Linux is like locking your car. Yes, a determined thief can steal it, but why would he bother? Most of the other cars in the car park are unlocked, some with the doors open, some even running with the keys in!

I used to say that I would never do online banking on a Windows box, now I am more paranoid, I'll only do it while booting from a live CD or USB key.