Because the information on a network is sharable, networks are very susceptible to unauthorized intruders. In order to prevent unauthorized access to use the services of the network, the user identifies self by providing name and a confidential password.
The NOS than allows access only if both the name and password are correct, This process is known as Login. The user is said to be logging into the network. The name which the user uses to enter the network is called the login-ID or login name.