Following this article on Neowin, this is from Ars Technica:
"I just saw over at /. that the Doom III E3 alpha has been leaked. Obviously the Alpha is considerably out of date, but that hasn"t stopped a flood of people from trying to find places to download the code to check it out. Personally, if Carmack doesn"t think it"s ready for us to play with, then I"m happy to stick with Bombing Run for the meantime. It does mean that there"s a flurry of new screenshots out there for you to drool over, if you want.
Some Ars readers have pointed out that a French enthusiast site is naming ATI as the source of the leak, but that has not been confirmed, and may be simple speculation (or an attempt to malign the company, for that matter). Nevertheless, a number of sites are carrying an alleged IRC discussion with Xian of id who "said" that id can tell where the leak stemmed from because of in-house watermarking. Of course, spoofing your identity on IRC is about the easiest thing to do in the world. /nick OJ_Simpson n I really did do it! Meanwhile, UT2003Online is claiming that the multiplayer code actually works, but details are not yet available. From all indications, this was a true leak, thus the game is warez until we hear otherwise."
UPDATE: It seems like UT2003Online"s page dedicated to Doom 3 has been defaced.