Abstract: A means for copyprotecting disks. The present invention may be utilized with both blank and programmed disks. Permanent random input/output errors such as an absence of magnetic material are placed on a disk by removal of material or by other methods and an input/output error trap routine or program is placed on the disk. The input/output error trap routine or program runs during the use of the user software program. A copied disk will not contain the permanent input/output error that existed on the original target disk because the input/output errors are not reproduced because they are not machine readable. When the copied disk is run, the input/output error trap routine cannot locate the permanent input/output error that existed on the original target disk.