I created an account to help Windows 10 users understand the issue with the failed initial firmware update: Digital Driver Signatures.
To resolve, in Windows 10:
Hold shift while clicking the reset button.
Click Troubleshoot.
Click 7 - Disable Digitial Signature Enforcement.
This allows you to run the driver install program successfully. While there, run the Android tool and follow instructions for the initial firmware install.
When you restart, driver signatures will be enabled again.