Time control is an effective barrier against potential hacking over weekends and other times when the system is left unattended. A hacker needs a period in which he or she can spend time quietly trying to break the passwords of users on the system. Time control is a good idea for a number of functions. In the first place, we can differentiate between the different computers within the organization. Some computers might only be used between 08:00 and 16:00. Once these computers are switched off at 16:00, it will not be possible to start them again until 08:00 the next morning. Users within an organization have different requirements. Some users require access to their computer between certain times, while others need 24 hour access. It should be possible to define this in the user registration component of the access control system. Time control may also be appropriate for applications. Some companies might want to introduce time control to define when it is possible to play computer games. Others might impose time restrictions on when specific applications can be started from the network. Many people are attracted to the idea of time control when they first hear about it. Experience shows, however, that the function limits the users' flexibility in their daily work. For example, imagine the situation where an employee is going on a business trip and realizes the evening before he leaves that he still needs some project files from the network. He will not be able to get the information he needs because the computer in the office is subject to time control and cannot be started until the morning. Be careful in applying time control, but even so, an access control product should provide the function, in order to guarantee flexibility for the future. A more effective form of time control is provided by checking when a user account starts, and when it expires. A user account could be granted for one week, after which the user will not be allowed to log on. It should also be possible to define a particular number of total logons to the system. This ensures that a user requesting a single access cannot log him/herself on more than once.