Mario Kart 8 and Splatoon on Wii U were taken offline at 11:30 pm EST on Thursday night. Both games remain that way at the time of typing this and it appears Nintendo has done so to address an issue that may have allowed hackers to access other people's consoles.
Reported by VGC, online services went down on Thursday night with the implication they will stay that way for a while. “We have identified vulnerabilities with online play for this network service and have begun temporary emergency maintenance,” a message on Nintendo's network maintenance site reads. “We expect an extended maintenance duration while we address these issues and have not determined when online play will resume.”
There's a belief a pretty serious hacking issue is to blame for this unscheduled downtime. Dataminer OatmealDome has suggested it's likely due to an exploit called ENLBufferPwn. A problem Nintendo has encountered before, it allows hackers to assume control of a console remotely and do what they like with it.
If that issue hitting Mario Kart 8 and Splatoon is indeed the reason both those games are currently offline, then it means anyone playing would have been exposed to hackers using their consoles, accessing their cameras and mics, and even stealing their credit card details. The exploit has previously been discovered and patched in Marion Kart 7 on the 3DS and has even needed to be scrubbed from Switch games including Animal Crossing: New Horizons and Mario Kart 8 Deluxe.
More bad news for anyone still using their Wii U as its online storefront will close for good later this month, along with the 3DS store. Online play for certain games, including Mario Kart 8, will remain available, so it's certainly worth Nintendo fixing this problem now so Wii U owners don't have another reason to give up on the console for good once most of the support for it ends in a few weeks.