It appears an early build of Gears of War 3 has leaked to the Internet, which allegedly includes the full campaign and multiplayer modes and may be an E3 build. After looking around, this turns out to be a developer build or "JTAG" version of the game, which means you need to have a special modified Xbox 360 or a dev kit to run it.
While this doesn't mean the game can be pirated in the traditional sense of the word, as it's not exactly easy to JTAG your console for the average person, it does mean that places like YouTube and streaming sites may become a haven for spoiler-rich Gears of War 3 content.
So be warned guys. If you want to remain spoiler-free, know that you may not get what you wish for when you click on a Gears of War 3 titled video or stream from now on. Even scrolling through the NeoGAF thread that first alerted us to the issue showed some potential spoilers, although I can't verify if they are real or not. I'm just going to pretend I never saw them.
Warning: Gears of War 3 leaked! [NeoGAF]