A FIDO U2F Security Key uses a specialized USB device to help secure your account with multi-factor authentication (MFA).
To set up FIDO U2F Security Key for MFA:
1. When you are verifying your identity, you will be prompted to select an MFA method. Select FIDO U2F Security Key. (You can also select FIDO U2F Security Key on the Sign In & Security tab of your account.)
2. You will be prompted to insert your security key into a USB port on your computer. Follow the prompts to complete the set-up process.
After set-up is complete, in order to use the FIDO U2F Security Key as an MFA option, just insert the key into a USB port during the sign-in process, and follow the onscreen instructions.
NOTE: U2F Security Keys are currently supported by Google Chrome since version 38 and Opera since version 40.