So my last name is Key, and my initials are C D, so in the mid-late 90s any time I was prompted to enter a CD Key I would always try “yes”. It worked at least half a dozen times.
In the Renegade BBS system, for like one minor version or so, you could authenticate to any account, including SysOp, by hitting Enter instead of providing a password. Of course, in Renegade and many BBSes, you could login with either your account name or ID, which was an auto-incrementing (the manual way) integer starting at "0", the Sysop. And I'm fairly certain that the problem wasn't triggered unless you logged in by ID, which few ever did.
On one Saturday nearly every BBS in my area code running that software was restoring from backup.
I stumbled upon it because I was "1" on another BBS[0] and accidentally popped "Enter" aiming for Shift when typing my password. After picking my jaw up from the table I called my buddy and told him to unplug the phone line. :)
[0] Actually, I had hacked up and substantially re-written from the leaked Telegard 2.5 source (whichever was the origin of Renegade's code) and the password validation code was insanity -- I was young enough to see hacking as mystical and suspected I'd found a cleverly hidden back-door so I rewrote the entire thing to be as "dumb as the rest of the password handling logic was"; I had heard, later, that there was something funny going on but I stopped playing with that code by then and the Internet quickly ended that world. In all likelihood, the original developers were doing something novel that I was totally unfamiliar with and I made it worse, but I like to think I "locked that up". :)