How do I remove this from my Windows 8 machine? Windows Defender didn't block it for some reason.
You've been infected with one of the latest versions of ransomware....unfortunately no antimalware program (including Windows Defender on Win 8) provides 100% protection.
Try going into Safe Mode, download/install/run Malwarebytes Free:
Go to www.malwarebytes.org and download, install, update and run the free version – just follow the prompts. Select Download Free – at the end of the installation
is a dialog with 3 check boxes: The first option is to Enable Free Trial of Malwarebytes Pro and you must uncheck the first option to install the free version without real time protection enabled. You may need to rename the installation file to 123.exe
or something similar to prevent the malware from disabling/blocking the installation. Or you might want to download the installation file to a flash drive or CD and then install Malwarebytes on the infected computer.