https://www.theregister.co.uk/2017/10/23/fyi_windows_10_ransomware_protection/

A below-the-radar security feature in the Windows 10 Fall Creators Update, aka version 1709 released last week, can stop ransomware and other file-scrambling nasties dead.

The controlled folder access mechanism within Windows Defender prevents suspicious applications from changing the contents of selected protected folders.