"Human error" is to blame for a recent leak of Mass Effect 3 on Xbox 360, according to developer BioWare. Microsoft apparently accidentally released the beta to Xbox Live users, though as soon as the mistake was discovered the file was obviously pulled.
Still, this didn't change the fact that many savy users managed to get into the rough version of the game and poke around revealing, among other things, that Mass Effect 3 will come packaged with three gameplay modes: Action Mode, Story Mode and RPG Mode. The latter appears to be the traditional way to play Mass Effect while Action Mode sets automatic responses for conversation, and Story Mode dumbs down the game's difficulty.
BioWare released a statement regarding the leak:
As most of you know by now, this evening an accidental leak occurred of some early Mass Effect 3 beta code. Microsoft has advised us that through human error at their end, content which was meant for internal beta testing was flagged incorrectly and released to individuals who had signed up for the beta of the Xbox Live dashboard update. It has since been taken down and deactivated.
We'd like to stress that the leaked code is in a rough, unfinished state and was not meant for public release. The content is not final, and is not reflective of the quality of the finished, polished game due for release [in March].
There's a hefty forum post over at NeoGAF
with lots of information pulled from this "human error", though we can't stress enough to you that it's spoiler-heavy - enter at your own risk.