To everyone complaining about Nintendo banning you for playing a leaked game online, you have no one to blame but yourself.
First of all, thinking that going online with a game that isn't officially released yet, would go unnoticed is being extremely naive. Don't you realize that Nintendo's servers keep logs of who's connected and when?
Second of all you're playing a pirated game which is a HUGE violation of Nintendo's TOS for online services. I'm not going to get into the whole ethical debate about whether piracy is right or wrong, just the fact that you should understand that when you violate the companies TOS they have every right legakly (abs otherwise) to ban you from accessing their network.
Put it into perspective, let's say hypothetically, you give an aquitance the password to your WiFi. All the sudden you notice your network is bogged down. Come to find out, the person you gave your password too is responsible (maybe they have a serious porn addiction and are constantly streaming it on 10 different screens all at once and torrenting etc, not a very realistic example, but trying to lighten the mood with some humor). Now aren't you well within your rights to change your WiFi password and not share the new one with said person. Just trying to make a point.
Again, not trying to debate the ethics a piracy itself, just saying that if you knowingly do something that Nintendo doesn't want you doing while accessing their online services,you're taking a big gamble and any ban that results from it, is no fault, but your own.
