Two-factor authentication (2FA) is an electronic authentication method that requires a user to present two or more pieces of evidence to an authentication mechanism to gain access to a website or application. It is a security system that requires two distinct forms of identification in order to access something. The two factors can be something the user knows (such as a password or PIN) and something the user possesses (such as a security token or smartphone) . Two-factor authentication adds an additional layer of security to the authentication process by making it harder for attackers to gain access to a persons devices or online accounts because, even if the victims password is hacked, a password alone is not enough to pass the authentication check.

Two-factor authentication is implemented to better protect both a users credentials and the resources the user can access. It is a proven way to prevent widespread cyberattacks and is recommended for all online accounts. Two-factor authentication is commonly used in web applications, online banking, and email services. It is also used in physical contexts, such as when a consumer is required to enter their zip code before using their credit card at a gas pump.

To enable two-factor authentication, the user is prompted to log in by the application or website, and then the user enters what they know (usually, username and password). The sites server finds a match and recognizes the user. The user is then prompted to provide the second factor, which can be a text with a code sent to their smartphone or other device, or a smartphone authenticator app, or biometrics using their fingerprint, face, or retina.

Two-factor authentication is not foolproof and may be ineffective against modern threats, like phishing, malware, and ATM skimming. However, it is a recommended security measure that can significantly improve the security of online accounts and devices.