Main goal of information system  security is to protect the information by preventing unauthorized users to log on system and provide to log on system only authorized users. For this goal, it is necessary to distinguish the authorized and unauthorized users. In this study, a security method, which doesn't require an extra hardware, was designed according to this goal. Also this system makes difficult to system logon even if the password is known by the hypothesis of distinguishing users according to their typing rhythms is possible.