It requires the use of the exploits in the Internet Browser, once you activate the exploit, your Wii U is hacked until you turn it off. There's a bunch of programmes out there that allow people to dump their game saves on their computer, modify it, then send it back to the Wii U. All Wii U hacks are done through the local network, with the computer sending the modifications to the Wii U as it loads the level. NWPlayer (the one who datamined Splatoon) has an exploit for 5.5.1 and someone who got access to it leaked it a few days ago. Essentially everyone now can use this exploit and modify their save data, so you can effectively give yourself all the shiny/pure gear you want, even if it's the unlikely roll. You really need to have a lot of knowledge about this stuff, as it is a lot more complicated than Wii hacking was. There are harmless hacks around too, that are client side and don't affect other players. One of those is an app called Splatoon Colorizer, which lets you change the colours of the ink and neutral objects to whatever you wish (red ink, black ink, white ink etc.). The thing is
@Lonely_Dolphin, even though we can all hack the Wii U right now, not everyone will understand how to modify the correct things in the save, corrupting it and losing everything. This is cheating and is definitely not fair for everyone else.
EDIT: As Lerrone just said, the abilities don't make a huge difference to the gameplay and performance of a player, so it isn't too bad, but it does make it easier to get perfect builds for weapons where gear combos don't work together at all.