Abstract: Optical discs, such as CDs, have been protected by the use of an authenticating signature which cannot be copied to another disc. A playing device is required to identify the existence of the authenticating signature in order to access the content of the disc. The authenticating signature may comprise bad sectors at known locations. CD writers now available to consumers allow error detection and error correction data to be specified and this has led to circumvention techniques designed to simulate an original disc. During the writing of a copy disc, bad sectors are identified and provided with alternative data together with incorrect error detection and error correction data. When the copy disc is played bad sectors are reported in exactly the same locations as reported by the original disc thereby enabling the disc to be played even though it is a copy.