Back a bit (yes, I am dating myself here), I worked for a floppy disk duplicating company that was hired by a certain software company to attempt to duplicate the disks with built-in copy protection. The customer provided a routine where they would have the end-users' disk controllers read a hidden half sector at the end of a half-sized normal ninth sector, I think was the gist of that particular scheme.

If I remember correctly, they had typed some example code in plain ascii, so we obliged with the typical "help, I'm being held captive in a Chinese disk duplication company." Which was almost true, as the owners of our company were of Chinese decent. And in my defense, we did have a number of all-nighters (with Pizza) when another software company would call us with a sudden "we've changed the masters - erase and re-dupe whatever you have)." I was younger, then...

Anyway, a few messages were passed back and forth this way, before we got back to serious business and implemented the copy protection scheme. Not really a virus, but still geeky fun.

Did you know that 8" floppy disks had excellent aerobatic qualities when flung from the top of a building? The trick was holding them by the corner during the wind-up...