Re: Machine Operating System
Kinda.
Going back a bit so the details are a bit (a lot, actually) hazy. You could put a non-printable character in the disc name, which had the effect of stopping a directory listing at that point. With the appropriate text before that character you could display all sorts of nasty/scary/downright annoying messages, and lock people out unless they knew what file they needed to run.
It became a bit of a manual virus, it quickly spread around the discs for my school's BBCs.