Abstract: This Protection System, for PC Software stored in CD-ROM, prevents the illegal copying (hacking) with negligible cost increase of the protected Application. The same CD-ROM that contains the Application Software serves as a "protection key". The CD-ROM disk undergoes a special treatment during its production phase that results in the generation of the Inspection Ring. This system uses a special method for the verification of the authenticity of the Inspection Ring. The existence of the Inspection Ring along with the use of the authenticity verification procedure make impossible the copying of the CD-ROM disk even with the most advanced recording equipment. This system has many advantages over other protection methods like: excellent protection, transparency to the end-user and very low cost since the "protection-key" is the same CD-ROM disk that contains the Application.