SOFTWARE COPY PROTECTION BY CONTROLLED UNRELIABILITY.

Unauthorized copying of software programs on a magnetic disk is prevented by deliberately creating on the disk a data area which cannot be reliably read. Multiple attempts to read the data area will not produce identical results. A routine is embedded within the software which performs multiple reads on the data area every time a program is loaded from the disk. If multiple reads on the data area produce identical results, then this is an indication that the disk being read is a copy and not the original disk.