title: How to prevent multiple user login with same user name and password?
body: <p>I am developing secure login system with php. I want to prevent multiple login for user with same username and password. With my script user can login on account from different browsers or from different IP with same username and password. I need to add some column on my database. When user logged in field becomes 1, and account is locked, when user logged out account is unlocked. But what if user close the browser without logout? </p>