At the security screen, shown above, click on the Task Manager button. This will launch the Windows 10/8 Task Manager as shown below. You now want to click on the More Details option to show the full list of running processes.
Select the process, or program, you wish to terminate by left-clicking on it once so it becomes highlighted as shown in the image above. Once you select a process, the End Task button will become available. To terminate the program, click on the End Task button and the program will be terminated.