Copyrighted software may be executed only on an authorized computer by using a protection mechanism to restrain software to a designated machine. The protection mechanism includes a CIN (Computer Identification Number) reader and a CIN verifier. The CIN reader comprises a function call which reads CINs from the computer where the copyrighted software is intended to execute, and a converter which converts CINs to encrypted CINs. The CIN verifier comprises the encrypted authorized CINs and logic. The CIN may comprise the serial number of a computer chip, the serial number of a hard disk, the serial number of a computer operating system or the like. Protection mechanisms may be integrated into the copyrighted software at stop points by compiling the software source code or revising the executable code of the software. When the resulting protected software is processed on a computer, the protection mechanisms are executed at the stop points. The CIN verifiers then compare the encrypted authorized CINs with the encrypted read-in CINs. If the comparisons of the encrypted CINs match, the copyrighted software continues running. However, if the encrypted CINs are different, the protected software stops running and sends out a warning message.