The invention relates to a security device for data carriers which may be or is secured onto or within a data carrier or its housing, and in which data may be exchanged, especially bidirectionally, with the security device, by means of a read/write device especially provided for the data carrier. The invention furthermore relates to a data carrier, especially optical data carriers with such a security device, as well as a process for securing data carriers against unauthorized copying, wherein data recorded on an electronic security device installed upon or in a data carrier, are processed by the security device and the outcome of such processing is read out from the security device.