Mine was diving into the memory stack of LJpegViewer Pro iirc - I had a license key taped to a floppy that had long since vanished, but using a debugger and hex

Mine was diving into the memory stack of LJpegViewer Pro iirc - I had a license key taped to a floppy that had long since vanished, but using a debugger and hex editor to treat any key as valid was fairly straightforward and gave me a real distaste for assembly