Authorized disks made in accordance with the invention are physically distinguishable from the blank disks which would be used for making unauthorized copies. A security check procedure is included in the initializing routine that is recorded on the authorized disk and that is executed prior to the reading out of any of the protected data. The security check procedure involves a test to determine whether the disk on which it has been recorded has or does not have the physical fingerprint that is the hallmark of an authorized disk. If the fingerprint is absent, the security check procedure prevents the protected material from being read out. Thus, unauthorized copies are useless because the protected data cannot be read out of them.