How to prevent a user from having multiple instances of the Same Web application

Question

I\'m wondering if it is possible to determine if a user already has a web browser open to the web application I\'m working on. It seems that they can open several instances

Answer 1

You could check if a the user has more than one active session. This might work, but could be problematic since there's no good way to determine if a session is really active or not.