Data security system for a vehicle navigation system, comprising: - enabling/disabling means for enabling or disabling a data transfer from a data memory comprising navigation data to be transmitted to a data storing unit of the navigation system, wherein the data memory is a removable data memory which can be removably arranged in the navigation system, the data storing unit of the navigation device being a fixed disk, - means for identifying a vehicle or navigation system identification code, - a comparison unit for comparing a vehicle or navigation system identification code stored on the enabling/disabling means to the respective identification code of the vehicle or navigation system identified by the means for identifying the identification code, wherein the enabling/disabling means enables or disables the data transfer in dependence on the comparison, - control means for verifying whether any vehicle or navigation system identification code is stored on the enabling/disabling means, and wherein, if a vehicle or navigation system identification code is not stored on the enabling/disabling means, a writing unit writes the vehicle or navigation system identification code retrieved from the means for identifying the identification code in the enabling/disabling means, wherein the enabling/disabling means stores the release number of the navigation data to be transmitted to the data storing unit and the status of the data transfer to the data storing unit, wherein the enabling/disabling means enables the data transfer to the data storing unit if the two vehicle identification codes or the two navigation system identification codes coincide, and disables the data transfer if the two vehicle identification codes or the two navigation system identification codes do not coincide. - enabling/disabling means for enabling or disabling a data transfer from a data memory comprising navigation data to be transmitted to a data storing unit of the navigation system, wherein the data memory is a removable data memory which can be removably arranged in the navigation system, the data storing unit of the navigation device being a fixed disk, - means for identifying a vehicle or navigation system identification code, - a comparison unit for comparing a vehicle or navigation system identification code stored on the enabling/disabling means to the respective identification code of the vehicle or navigation system identified by the means for identifying the identification code, wherein the enabling/disabling means enables or disables the data transfer in dependence on the comparison, - control means for verifying whether any vehicle or navigation system identification code is stored on the enabling/disabling means, and wherein, if a vehicle or navigation system identification code is not stored on the enabling/disabling means, a writing unit writes the vehicle or navigation system identification code retrieved from the means for identifying the identification code in the enabling/disabling means, wherein the enabling/disabling means stores the release number of the navigation data to be transmitted to the data storing unit and the status of the data transfer to the data storing unit, wherein the enabling/disabling means enables the data transfer to the data storing unit if the two vehicle identification codes or the two navigation system identification codes coincide, and disables the data transfer if the two vehicle identification codes or the two navigation system identification codes do not coincide.