You may not know it, but if you Tweet, have an iPhone or a Facebook account, chances are you have already used some form of Two Tier Authentication. Two-factor authentication or 2FA adds an extra step to your log-in procedure. In the past, to log in to your account, you would be asked to enter a username and password. This sign-in process is an example of a single-factor authentication. Basically, the first step in the authentication process asks you for something you know: your password. In a 2 Tier process, you will also be asked for something you have: your phone using a text message, or perhaps an alternate email address. You will then be prompted to enter a verification code. Adding this second layer of security makes your account stronger and less vulnerable to hackers.
Interested in learning more? Check out this terrific overview of 2-Step Verification from Google.
Remember Google is not the only vendor using 2FA; it is now commonplace with Apple, Microsoft, and many other cloud based services.
Finally, be sure to track and monitor the phone numbers or email addresses you use for your 2 tier authentication. Should you change this phone number or email address, you will need to update your account.