A copy-protection scheme is implemented for software which may be stored on a magnetic storage medium such as a disk. The medium is comprised of sections which are divided into subsections, with an original having indicia on at least one subsection of at least one section that is not modifiable by the medium write process, with a copy having no such indicia, or having indicia in a different pattern. A product program may be stored on the medium, and is executable only if the particular medium is an original. A medium test program may also be stored on the particular medium, and is used to test if the medium is an original or a copy. The test program writes the sections with a test pattern which generates a change in the pattern of magnetic domains of the medium, a subsection at a time, with a subsection responding to the test pattern only in the absence of indicia thereon, to form a stored pattern on the given section. An expected pattern and the stored pattern are compared at least a subsection at a time to determine if corresponding subsections have a predetermined pattern of magnetic domains. The product program is executed only in response to the comparison determining that corresponding subsections have predetermined patterns of magnetic domains which is indicative of the presence of said indicia, and the particular medium being an original.