A post by id Software's John Carmack to a thread called Doom 3 Alpha Leaked on Slashdot has confirmation of the fact that an early build of DOOM III has been leaked. Here's the post, which vaguely hints at the source of the release:
All trademarks are properties of their respective owners.
News CGI copyright © 1999-2014 James "furn" Furness &
All rights reserved.
Chatbear v1.4.0/blue++: Page generated 24 October 2014, 15:07.