Many Mac OS users might assume that their computer is exempt from things like ransomware attacks and think that their system is somehow essentially “secure.” It is true that it’s less likely for a Mac OS user to be attacked or infected by malware than a Windows user, but this has nothing to do with the level of vulnerability in the operating system. It is largely caused by the fact that over 90% of personal computers run on Microsoft Windows and only around 6% on Apple Mac OS.

https://blog.fortinet.com/2017/06/09/macransom-offered-as-ransomware-as-a-service