Two-factor authentication is an optional additional level of security that can be applied to "Runescape" accounts. When a player successfully enters a password from an unrecognized or untrusted computer, he is asked to enter a code sent to his mobile phone. This two-factor authentication mechanism is used to make it more difficult for hijackers, phishers and other unscrupulous people to steal player accounts.
In the broadest sense, two-factor authentication is any technique that requires a user to present two separate pieces of information to prove that he is who he claims to be. This idea is also applied offline. A classic example of two-factor authentication is the use of bank PINs, where the bank card and PIN must be used together to withdraw money at a bank or when making a card purchase. "Runescape" also has an optional bank PIN feature that is used to protect a player's in-game stored items in a similar way. In this sense, "Runescape" has two-factor authentication to protect unauthorized access to player accounts, and even stronger three-factor authentication for the virtual bank accounts.
"Runescape" is not alone in providing multi-factor authentication options for players, other games often provide these authentication solutions as well. Valve provides Steam Guard to its users, which provides two-factor authentication for games available on the Steam platform. Two-factor solutions are also offered for social media users on Facebook, Google+ and Twitter.