The invention relates to a controller for a wind turbine with an operating software for operating the wind turbine, wherein the operating software is set up to regulate or control at least an electrical output of a wind turbine generator, a speed of a wind turbine rotor, an azimuth angle of a wind turbine nacelle, and a pitch angle of at least one rotor blade of the wind turbine rotor, wherein the operating software comprises a core module and at least one customer application. The customer application is set up to determine a parameter, in particular a control variable, in particular a target value, depending on at least one function of the customer application, and provide it for the core module. The core module is set up to detect and/or predict a load acting on the wind turbine during an operation of the wind turbine, and in a case where a detected or predicted load lies below a predefined load limit, to operate the wind turbine as a function of the parameter provided by the customer application, and in a case where a detected or predicted load exceeds the predefined load limit, to adjust the prepared parameter and leave the wind turbine unconsidered as a function of the adjusted parameter or the provided parameter, and operate the wind turbine with a parameter determined in the core module. The controller further has a first programming interface and a second programming interface, wherein the first programming interface is set up to program the core module, in particular the load limits, and wherein the second programming interface is set up to program the customer applications, in particular their function, and prevent the core module from being reprogrammed via the second programming interface. The invention further relates to a method for a controller and a computer program product.