In an extranet or intranet website you may want to limit the user’s access to a unique machine at at time.
One way to do that is to have a table with the logged users and check the new user against that table and block his access if there is already one instance of that user logged in.
But, what if the user shutdown the browser, or the computer, without logging out of the system ? In that case, he will never be able to loggin again, unless he calls support to clear his record or waits until the session time out.
Download the sample code here.