Two-factor authentication (2FA) is a security layer for ProtonMail email accounts. When the two-factor authentication is enabled on your ProtonMail, you will be asked to enter a 6-digit code upon logging in. besides, Protonmail two factor authentication protects your account from being hacked. To enable Two-factor authentication for your ProtonMail account, you need to install the authenticator app on your device. There are various authenticator apps used to generate the 6-digit code. For Android and iOS, you can use the Authy, Google SAuthenticator, or FreeOTP app.