I was on the "have I been pwned" website, and I noticed that a certain Wii U site with "ISO" on it was breached in 2015. It claims that 458k accounts were leaked from it, which is, surprisingly, a LOT. Just to compare, the Wii U has sold 13.36 million. This would mean that about 3.4% of Wii U owners have signed up for the site, and are likely pirating games. This would also exclude users who use other methods, like USB Helper or Chaos, or non-pirating users with hacked Wii Us.