Earlier quoted context omitted.
People think Macs are virus-free because Apple spent years telling them were. Example ad, with John Hodgman as the Windows guy with a virus. https://www.youtube.com/watch?v=M3Z386vXrt4
This notion existed far before that ad came out. It's a combination of a few things: (1) why bother investing time and resources for a platform with around 10% of users and (2) OSX has had strong security mechanisms e.g Gatekeeper, XProtect, App Sandbox. Windows 10 is much better but unfortunately not everyone is on that OS yet.
Implying Windows 8.1 has security problems... what are they?