Nintendo of America’s official website announced that due to the discovery of security issues, it temporarily shut down the multiplayer servers of the two games “Mario Kart 8” and “Splatoon” earlier today.
This means that on the Nintendo Wii U game console, players can no longer play these two games online. The contents of the Nintendo support website are as follows:
"This web service is currently unavailable due to urgent maintenance due to an online game-related vulnerability. It is not yet confirmed when this web service will be restored, and we apologize for the inconvenience."