This is an individual who is not authorized to use the computer and who penetrates a system s access controls to exploit a legitimate user s account. The misfeasor is a legitimate user who access data, programs, or resources for which such access is not authorized. A clandestine user is who seizes supervisory control of the system and uses this control to evade auditing and access controls or to suppress audit collection. The intruder needs information in the form of a user password. Then, he can log in to a system and exercise all the privileges accorded to the legitimate user.
Some effort is needed for a potential intruder to learn passwords.
Collect information about users, such as full names, names of spouses, children, books in office, etc Try user s phone numbers. Social security numbers, room numbers License plate numbers Use a Trojan horse Guessing attacks are feasible, and indeed highly effective, when a large number of guesses can be attempted, and each guess verified, without the guess process being detectable. The professional intruder is unlikely to try those crude guessing methods. The front line of defense against intruders is the password system. The password serves to authenticate the ID of the individual logging on to the system.