Add another step to the process of single factor authentication; requires an additional credential. For example, when you log into your banks website, it may send a text message to your mobile phone that consists of a randomly generated code. The code is unique to you and into this moment in time. Then enter the code along with your username and password to gain access to the site. 2F a is considered more secure because it's likely that you're the only person in possession of your phone. Biometric devices, such as the fingerprint ID sensors on some smart phones, and also function as a second level of authentication