It doesn't need to be anything complicated. If you just re-upload the original code to a new location, and then Nintendo has to start the entire process of tracking the uploader down in order to threaten them.
Ironically for a video games company Nintendo don't really seem to quite understand how the modern world works.
I've worked at plenty of places which have made it fairly clear that the only way you can progress up in the company is to work out of hours. Extremely illegal business practice but they did it anyway.
One of the places was a law firm, because lawyers always think that they know how to break the law.