Borderlands 2 developer Gearbox has warned Xbox users to steer clear of public games for the moment. It’s a response to a bizarre virus-like bug that dying in the game really does kill off a character.

The problem comes about from a hidden feature in the game, dubbed “badass” mode from the setting “IsBadassModeSaveGame”, that is switched off by default. Players who have modded their console (whether that to play third-party games or bypass anti-piracy protections) can switch the mode on.

The upside of the mode is that you can make your character far more powerful and get hold of special weapons. The downside is if your character dies, that’s it: there’s no respawning and the character’s save files are deleted from your console.

In and of itself, that’s not a big issue: players can simply make the decision whether to take the risk of losing a carefully-crafted player for the sake of extra powers. The problem is that if any player in a multiplayer game has the mode switched on, it’s automatically activated (without any warning or notification) for all players in the game, regardless of whether their console is modded.

Gearbox is still working on a fix. In the meantime it says to only play multiplayer with people you know and trust, in non-public sessions. It’s also suggesting using the “save and quit” option to protect existing characters. If your character does die, select “Continue” from the main menu rather than waiting to respawn. This only applies to the Xbox 360: PS3 and PC players have nothing to worry about.

There’s no official explanation yet for why the mode was added to the game in the first place. Most likely Gearbox considered the mode, abandoned it, but failed to remove it and left it in place complete with bugs.