A method for operating a mobile device, not assigned to a motor vehicle, via an electronic device with a display and operator control device of the motor vehicle is made available. The program has program parts for a user interface and for operator control sequences which are assigned a digital certificate. The user interface comprises fixed areas for displaying variable contents. The program parts are transmitted together with the digital certificate to the electronic device of the motor vehicle and are carried out when the certificate is successfully checked. The transmission of data without protection by a digital certificate is restricted to the variable contents for display in the fixed areas of the user interface.