;) In my ASP .Net web application, the customer has the following requirement. Whenever user tries to close the browser by using the X at the top (the hard close), I want to throw a message popup to user saying that they have not logged out of the application. Are you sure to close? And I want to give them Yes/No options so that if they click on yes, I will let them close otherwise the browser stays open. How can I acheive this?