Two Factor Authentication Premium (TFA) is a tried-and-tested way to secure your WordPress site from unwanted logins.

By default, WordPress is protected only by a password. Once somebody guesses your password, they have all access. "Two Factor" security is about adding a second factor. This plugin uses the most popular implementation of TFA: one-time codes that are shown on your phone/tablet/other device, but which do not require you to be connected to a network (i.e. you don’t need to be online/receiving SMSes, etc.)