A public service announcement: Be very careful when playing Splatoon online.
A hacker has managed to work their way into Splatoon and their presence may result in a permanent loss of your character.
The signs of the hacker is a player name beginning with K and containing several numbers, who is playing as an Octoling with the unreleased Hydra Splatling weapon. If you leave the room before they do, it will corrupt the plaza by preventing your character from loading, necessitating the deletion of the save file. If the character is spotted you have to keep playing until one match after they leave your lobby.
Anyone who has additional details on the hacker is encouraged to contact gotnews at nintendoworldreport dot com and also forward the information to Nintendo. Participation in a Splatfest may allow for the corruption to be fixed but this is not confirmed.
UPDATE October 1: The player name to watch for is "K9516B". (Thanks to MetalSmasher86 in Talkback for finding this.)