Currently, there are several warnings going about, mentioning that hackers are playing as Octolings and using unreleased weapons (such as the hydra splatling) online and that playing matches with them may cause your game to become temporarily unplayable.
The issue is caused if you finish a match with them and then quit playing before they quit playing. This could lead to your system trying to include their character on your plaza. But as they have currently locked items, the game doesn't load them, and locks you out of your plaza, preventing you from playing Splatoon.
There are 2 ways to avoid this:
1) If you see an octoling on the other team when the match starts, or during a match and know they were not in the group beforehand, disconnect from the game (turn the Wii U or your router off). This will prevent them being saved onto your plaza.
2) If you don't do this in the first match and play until the end of the match, you should keep playing until they leave the group, and then play one or two more matches without them, before quitting. This allos the game to overwrite their character with someone you played against more recently, instead of saving them to your plaza.
It may be possible to quit and go join another group (as that doesn't go via the plaza) if you play a full match against them, but so far it doesn't appear anyone has tried this.
If you do get affected by this, it is only temporary. When Splatfest comes around it resets your plaza and allows the game to load. This has been confirmed. (This is not a new issue, similar cases occured in August and a splatfest fixed the affect games then.)
Also, once the weapons / playable octolings become available the plaza will then be able to load normally.
. I hope Nintendo fixes this hack. If you play with this hacker, and leave the room before he does, IT WILL CORRUPT YOUR SAVE DATA!
Since I already erased my game due to the situation I dont think a splatfest will recover my data now. I am not sure if I can even play in the splatfest now unless I can be prepared for it when it starts. If I can get my weapon (the N Zap 89) before the splatfest start I should be prepared regardless if my level was 32 or 1. Do you know if I can get this weapon right away or if not what level it unlocks at? 
