The WannaCry cyber-attack all over the world in May, 2017 is still fresh in our minds. The malware encrypted and rendered useless hundreds of thousands of computers in over 150 countries. As a measure against ransomware, Microsoft introduced the function “Ransomware protection” in “Windows 10 Fall Creators Update”. How does this function work? Is it really effective? In this talk, I will explain the operation principles of “Controlled folder access” of “Ransomware protection” through demonstration video. Then I show the requirements to avoid this function, and describe that this function can be avoided very easily. And I will ask you that we may have to reconsider the definition of vulnerability.