A bug in the popular Borderlands 2 video game is causing grief for some Xbox 360 players after attackers unleashed a virally spreading exploit that can permanently kill off characters.

Last week, Gearbox community manager Chris Faylor warned of an "external application to maliciously disrupt the experience and sabotage characters" on Xbox 360 systems. Gearbox engineers have shipped an update to Microsoft that will be released as soon as possible. In the meantime, Faylor advised customers playing Borderlands 2 on Xbox consoles to "consider playing online with trusted individuals in non-public sessions." Over the weekend, the same user forum remained active, with some participants reporting their characters, vehicles, and skins were erased. "Kind of upsetting that I get punished because other people like to ruin the game," one user lamented.

The sabotage campaign, according to a post by someone with the user name pclifford, could be enabled by modifying a setting known as "IsBadassModeSaveGame" included in Borderlands 2. It's disabled by default, but users who modify their Xbox systems can turn it on, allowing them to enter what's known as "badass mode." Increasing the impact of the attack, Xbox systems will enable the mode when they encounter other modified systems, causing the campaign to spread wider than it would otherwise.

"In a nutshell, once your character is in 'badass' mode, playing [with] other people will force their characters into this mode too," the writer of one follow-up post claimed. "Hence the 'virus' explanation—as with a cold or the flu in real life, you can spread it to other people before noticing the symptoms, and without any evil intent. They in turn can spread it on to others."

According to users in the forum, once the hidden mode is turned on Borderlands 2, characters are deleted when they die during play.

Faylor advised users to always select "Save and Quit" from within the game's pause menu while their character is alive. "If after the death of their character players find themselves at the main menu of Borderlands 2 instead of respawning in-game, be sure to immediately select 'Continue' to resume playing as that character."

Gearbox officials have yet to provide advice for users who have already lost characters as a result of the attack.