Kind of a necro-post, but I feel I have relevant information to add to this
Windows Defender likely would not have protected you from this to begin with unless it's older Ransomware. WD has about a 70% detection rate, so while it's not great, it's better than nothing. However there's nothing more dangerous than a false sense of security. I digress.
Crypto ransomware can be defeated by following some of the IT best practices for the corporate world. What I mean by this is, bottom line, software like this can only modify the files that the infected account has rights to. So take your rights away.
Least Privilege Principal - Anyone who is familiar with the Unix or Linux operating environments knows this mantra by heart: NEVER USE ROOT FOR EVERYDAY USE. Logging on as root to do your everyday computing is the worst idea when security is concerned. Microsoft, however, encourages this as user accounts are created as administrators by default. If you're logged in as an admin, any virus or malware that's infected you has the same rights you do. When setting windows up for the first time, it's important to create an admin account, sure. With the admin account, create the account you're going to use for every day stuff. Log out of admin, log into normal user account and never log back in as admin again. If windows needs admin rights to do something, you will be prompted for the password of your admin account. If you start getting prompted for credentials for no reason, something is going on that you need to investigate.
Keep essential files away from your main system - If you want to go the extra paranoid route, you can always keep an older, non used system on your network with all of your drives on it. On the older system, create an account with the exact same username/password as your admin account, and use SMB to access those drives across the network. The first time you hit those drives, it will force you to authenticate. Give your admin account read only access from the other system. This will keep cryptoware from being able to affect those files.
All of this sounds super convoluted, however in IT security, there is no such thing as a perfect balance between convenience and security.