sourceAccording to Mathieulh, the recent build of Gears of War 3 that appeared on torrent sites earlier this month may have been inadvertently leaked by Microsoft themselves. A Google query for codify.com xbox will reveal Microsofts Xbox 360 Codify page which may have, at one point, offered up Gears of War 3 for grabs. The offending pages and files have been taken offline, however Google Cache has record accessible GOW3 files on the site.
The incriminating results included a page that revealed the directory for the Gears of War 3 files, only marking it confidential in the folder name and providing no other securities against unauthorized access. Yet another page revealed game assets. Its unclear if this was the source of the leak, however it is a possibility given that the Gears of War 3 Confidential directory was accessible at one time by the average joe."
http://xbox.codify.com/GOW3/GEARS-OF-WAR-3-CONFIDENTIAL/Gears-3-build/UnrealEngine3/Binaries/Win32/
(removed/dead) but i've linked it to the google search.
xbox.codify.com still works, some files on it.