A method for storing or reading data in a memory array of a transponder and a corresponding transponder, read/write device and program element is described. Therein, a data structure for storing data within the memory array is defined by a predetermined protocol. The data structure comprises: a header data block including predefined header data; an application data block for storing application data; a memory control data block including a reservation indicator for indicating a reserved partial memory area of the memory array where, in accordance with the predetermined protocol, application data cannot be read or written by a protocol compliant reader device. The method for storing data comprises storing additional application data in the reserved partial memory area. Thereby, memory areas which, according to the predetermined protocol, are not used can be used for new applications, data can be hidden in these areas such that they cannot be read by protocol compliant reader devices and the data structure read or written by the method of the invention is compatible with the former predetermined protocol.