Now-a-days, social networking sites are becoming very popular. The most important task is to secure them. User authentication is used to confirm the user identity on systems to perform a given operation. Traditionally, people use passwords for creating their account. Almost everyone today has about 10 - 25 password protected accounts (Facebook, Gmail, LinkedIn to account for few). More accounts mean more passwords which are difficult to remember. People compensate by using the same password for various accounts, and by choosing passwords that they can remember easily.