TFS uses multi-factor authentication (MFA) to help us verify your identity. MFA is an authentication method used to help prevent unauthorized access to your account by relying on two or more independent factors to verify your identity.
With MFA in place, end users are required to supply two or more independent factors to verify your identity. For example, you may be asked to enter your password and a verification code. A verification code is a one-time use code that we send to you by email, text or phone call.
For additional security, you may choose to receive a verification code each time you login. You may choose to add this two step verification process when you register your account or anytime from the Profile/Security settings within your account. Although this two step verification process is optional, we may still require a verification code at login in certain instances such as if your risk profile is high, based on your typical login and usage profile and/or you have indicated that you are sharing your device with others.