1. In a computer program protection method intended to distinguish between computer programs recorded on a bona fide recording medium and corresponding programs copied from such bona fide medium onto a similar recording medium, the steps of: a. Writing a code signal at a predetermined location in said information recording medium in accordance with an instruction incorporated within the program to be protected; b. Verifying in the computer the code signal stored at said predetermined location; and c. The step of utilizing as said bona fide recording medium, a medium which is unresponsive to such instruction to write said code signal at said predetermined location.