End specific session outside the current session

Hello people,
I am working on a business web application at the moment.
I would like to check if someone tries to access the application with the same username from a different browser/pc/etc. All usernames and passwords are stored in a MSSQL db.
What I am doing at the moment is: In the global.asax-file in Application_start(..) I initialize Application["UserList"] = null;


Then in Session_start(...) I add the current user with


Application["UserList"] = new UserObject(username, Session.SessionID);

Now with every user that logs in I can check whether he is allready in ( in that case, he won't be able to log in, he'll be redirected to the login page ). Let's say it's the same user who wants to login but for some reason he wants to start the application from a different pc, maybe in a different building. ...