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Something you know - This is anything you might need to remember and type or say. It's something you have to recall from memory. An example might be your mother’s maiden name, a password, a passphrase, or PIN.
Something you have - This includes all items that are physical objects that you must have. Specifically it includes the use of to provide a time based PIN or other generated number that must be inputted to verify someone’s identity. An example might be this hardware token: or the
Something you are - Includes using a part of the body that can be used for verification (biometric data), like fingerprints, palm scanning, facial recognition, retina scan, iris scan, voice recognition. This works because each person is unique, but it can be invasive because it may reveal information about an individual’s health concerns. An example might be this
Somewhere you are - Uses location based data to determine if someone is in the correct vicinity to access data. An example of location restriction using Azure is portrayed in this .
Time restrictions - Time can be used as part of MFA because data assets might have restrictions about when they can be accessed. If access attempts occur outside the time window, someone may be disqualified. An example in which time might be used is in a (TOTP). Per , a TOTP “is a passcode valid for 30 to 90 seconds that has been generated using the value of the Shared Secret and system time.” This combines the “something you have” factor with time restrictions.
What are the pros and cons of MFA? A list by Mary Shacklett of Transworld Data at this shows it can be complicated, but worth it.
Importantly, there are many data breaches that occurred as a result of not using multi factor authentication. An by Jean Shin includes information about several of these breaches which affected Target and Equifax among others.