Abstract: An apparatus for accessing a controller, wherein a first control program for controlling a process runs in the controller and the process is actively controlled by a process image of first input signals, which are received by the controller, and first output signals, which are output to the process by the controller. The apparatus comprises an interface for interchanging data with the controller and a computation unit for executing program code instructions of a second control program. The apparatus also includes a comparison device which is configured such that the first output signals can be compared with second output signals and provide a comparison result, where the second output signals can be generated by the second control program, the program code instructions of which differ from the program code instructions of the first control program.