A client computer and a server computer communicate via HTTP. The client computer uses a standard HTTP-browser. Substantially simultaneously with establishing a session by allocating a resource at the server computer, the server computer sends a termination instruction to the browser. The instruction remains unexecuted in the browser during the whole session. In the event that the server computer terminates the session (such as upon unloading the instruction from the browser), the browser causes the server computer to de-allocate the resource.