As a Mac user I could be accused of rubbing it in when it comes to Windows security problems. So are the chickens coming home to roost? Could it be that Mac users haven't built up the necessary 'immunity' to ward off problems when they come?

Maybe, but not likely. I don't thinks a 'whatever doesn't kill us, makes us stronger' approach applies to computer users. Despite being barraged for years by mal-ware, the average Windows user still doesn't have the faintest idea how security works.