1. In a window based computer controlled display system, said system comprising a display, a first application controlling a first window on the display, a second application controlling a second window on the display and a cursor located within the first window on the display, a method for transferring control between the first application and second application comprising the steps of: providing a at least one first handler process through which the first application controls the first window and at least one second handler process through which the second application controls the second window; determining the position of the cursor; and if the cursor has moved from the first window to the second window, issuing a first message to the second application program that the second application program is to activate, switching execution from the first handler process to the second handler process, determining whether the second application is activated, and if it is determined that the second application is valid and activated, issuing a second message to the first application to transfer control to said second application and deactivate; wherein said second application program assumes control.