The Story of the Game Genie, a Cheat Device Nintendo Tried (and Failed) to Kill(nintendolife.com)

  They even had Shigeru Miyamoto in court - he came to San Francisco.
  They were saying that because the player was plugging in the
  interface and making Mario jump higher, the player was making a
  derivative work, and we were helping him infringe copyright. In the
  end, the judge said it was not permanently changed when you
  unplugged it, and for a derivative work to exist it has to be
  permanent.
  
  [...] Some of the team's tactics were quite interesting,
  highlighting the hypocrisy of Nintendo, as Menzies explains. "I
  helped with the lawsuit by creating non-Game Genie codes that could
  be entered into an official Nintendo game's own password system and
  would crash it, cause graphical corruption, weird behaviour, and so
  on. Basically all of the things that Nintendo's lawsuit accused
  Game Genie of doing, so we could say to the judge 'look, this isn't
  anything to do with us, Nintendo's games do this on their own, it's
  just how video games work'."