Some users log on to the network and then don't log off for months. This is a prominent security hole, as when that user leaves her desk, she still is authenticated to the network with her credentials. Malicious people can use this to do destructive things: delete and transfer files, plant a "root kit" or backdoor program, or change passwords.
You can make automatic logoff work in two ways: first, each valid user needs to have a time when she is not permitted to log on. This can be sometime in the early morning, perhaps 3:00 to 3:30 a.m. Then, a change to the local security policy needs to be made so that when the user's logon time expires, she is not permitted to log on.
To set up a logon time restriction on a domain controller for an Active Directory-enabled domain, follow these steps:
Go to the Active Directory Users and Computers snap-in.
Expand the icon for your domain and click the Users container.
Right-click a user and select Properties.
Click the Account tab, and then click the Logon Hours ... button.
Select the appropriate region of time in the calendar block, and click the radio buttons to the right to either permit or deny logons during that time.
Click OK, and then OK once more to exit the user property sheet.