Authy

Cyber criminals can easily break into online accounts using leaked or stolen usernames and passwords — unless those accounts are also protected by a two-factor authen­ti­ca­tion step using the account owner’s personal device. Authy generates a unique time-dependent six-digit code for every login attempt and sends this code to a smartphone or any other device the account owner authorizes; using an API, any developer can add Authy to their apps. The free Authy service has been part of Twilio since 2015.