A security system for a vehicle has data transmitted to a central point for identity analysis e.g. for a global positioning system etc. The vehicle stored data is divided into data which relates to the type of vehicle, and which is common to other similar vehicles, and vehicle specific data. The vehicle type data is given an identifying code which is transmitted with the vehicle specific data. This ensures that a minimum of data transfer is needed without reducing the security. The system also ensures that the process can be performed even with some of the vehicle type data damaged.
