The Windows security model is not the broken mess it once was when properly used so the key problem is user behaviour particularly home users running as full admin, installing random crap without thinking about it (or simply not knowing any better), just clicking through any warnings they do get, and so forth.

If enough of that sort of user migrates over to Linux and kicks it into working the way they want (i.e. the bad way they used to work under Windows) you'll no doubt see the number of effective exploits balloon massively.

Jeff Wayne's Martians were right: "The problem is, of course, the humans."