Wow. 130 post before someone brought out that old timeworn 'popularity' canard. I believe that is some kind of record. The size of the installed base has little, if anything to do with making a given system a target for atttack. Google the "witty worm" for more information about that. The fact is, MS-windows is a stinking virus magnet. No other currently used operating system even comes close to it in terms of vulnerabilities.
The *real* problem is homogeneity of OSes. The *only* answer is heterogeneity.
Some Windows, some Macs, some Linux, some OS/2 ...
Throughout history monocultures have come crashing down with crushing consequences. Yet we never seem to learn.