Sorry, I wasn't clear. My "only compatible ..." left out "and does naughty things if otherwise."
Perhaps you'll like this example better? https://www.google.com/patents/US4577289 "Hardware key-on-disk system for copy-protecting magnetic storage media"
There are physical holes on the disk. "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."
If you have "insert key disk now", followed by a write to the disk, and then a verification, then a standard disk/non-key disk will get corrupted.
That 'bricks' non-brand floppies by design, under the aegis of copy protection.
There's been open source with back doors in it. Eg, Firebird had one that took about 6 months to detect, after source code release.
In listening to the various accounts of GPL enforcement, it isn't always easy to track down the actual vendor. Quoting from http://www.infoworld.com/article/2617579/open-source-softwar...:
> Always keen to shave the last few cents from their bill of materials, these manufacturers tend to procure their firmware from low-cost suppliers that have in turn delivered open source software without passing on its licensing terms. It can come as a surprise to the hardware manufacturer to discover a violation of the license terms.
While that's about incorrect use of licensing terms, it shows there's no reason why the manufacturers are aware of all of the code in the software they sell.
