As you're no doubt aware, some with early access to Pokémon Sun and Moon, whether through approved copies or grabbing them from early retail stock, couldn't behave themselves and promptly starting dropping spoilers online. Naturally the game files were also dumped, and a number of people started pirating the games; Nintendo has decided it's had enough.
What was interesting is that pirated copies were able to play online, so it seems a number with illegal copies were battling and using the online features. Whether deliberately playing online or not, plenty have started to post today that they're receiving bans from online services. This isn't just stopping online play in Sun and Moon, but reportedly in some cases blocks access to the eShop too; for those with games they want to re-download, for example, that's a major problem.
Though some assumed bans were only dropping on those that played their pirated copies online, some believe restrictions are also being placed on those that were staying away from online modes; after all, the game may be 'online' even when playing as normal - attempting to check its status, delivering event messages and so on.
After a lot of chatter on online forums like GBATemp and 4Chan - as per our usual policy we won't link to them directly - Nintendo provided a statement to Kotaku.
As a result of a number of Nintendo 3DS users using unauthorized versions of several games, and connecting to the official game servers in violation of our terms of service, these users' Nintendo 3DS systems that stored the unauthorized game code have been banned from Nintendo's online network effective immediately.
It's hard to feel too sympathetic for any that have received bans, we'd suggest. Some may have been 'trying it out' before buying the real game, but plenty will have simply been stealing copies. Some affected users are naturally concocting plans to get around the online restrictions, in any case.
This particular battle will never end.