Which of the following is a feature of two-factor authentication?

Two-factor authentication (2FA) enhances security by requiring users to confirm their identity through two different components before granting access. The essential feature of 2FA is that it incorporates a second verification method in addition to the primary authentication, typically something the user knows, like a password, and something the user has, like a smartphone or hardware token. This dual approach significantly increases security because, even if one factor (like the password) is compromised, the second factor serves as an additional barrier against unauthorized access.

In contrast, using a single device for authentication would not provide the layered security that 2FA is designed to deliver. Additionally, requiring only a username and password undermines security since it depends on a single factor, and eliminating the need for passwords altogether disregards a fundamental part of most authentication processes. Therefore, the correct answer highlights the integral aspect of two-factor authentication by emphasizing the necessity of a second verification method, which is crucial for mitigating risks associated with compromised credentials.