 Valve added Steam Guard functionality to the Steam client in March 2011 to protect against the hijacking of accounts via phishing schemes, one of the largest support issues Valve had at the time. Steam Guard was advertised to take advantage of the identity protection provided by Intel's second-generation Core processors and compatible motherboard hardware, which allows users to lock their account to a specific computer. Once locked, activity by that account on other computers must first be approved by the user on the locked computer. Support APIs for Steam Guard are available to third-party developers through Steamworks. Steam Guard also offers two-factor, risk-based authentication that uses a one-time verification code sent to a verified email address associated with the Steam account; this was later expanded to include two-factor authentication through the Steam mobile application, known as Steam Guard Mobile Authenticator. If Steam Guard is enabled, the verification code is sent each time the account is used from an unknown machine.
