Among the most notable elements of the leaked content is the original version of the Halo demo shown during the MacWorld 1999 event. The demo was presented by Steve Jobs, CEO of Apple, and Jason Jones, co-founder of Bungie and head of Halo, and showed us a very different game from Halo: Combat Evolved that was released in 2001 for Xbox under the Microsoft Game Studios label. The most notable change, not to mention that Microsoft bought Bungie and took exclusivity of the game from Apple, is that Halo was a third-person game for Mac.
It appears that the Halo demo was attempted to be restored for Halo: Master Chief Collection. With the leak, not only has it been recovered, but it is also playable on PC. The leaked material also includes levels and enemy designs from Halo 3 that were not included in the game, as well as various unfinished and discarded content from Halo 2, Halo: Reach and Halo: Master Chief Collection.
Halo presentation at MacWorld 1999.
The leak has not been claimed by anyone, but it seems to have come from a member of Digsite, a team made up of modders of the community who have recently collaborated with Halo Studios (343 Industries) at the launch of the Halo 2 demo shown at E3 2003. Digsite is a group made up of volunteers and several have recently left it as they cannot afford to continue their work without receiving payment from Microsoft. Former members of Digsite have confirmed that the material is legitimate, but have distanced themselves from its publication.
Following the leak, some of the people who have left Digsite have acknowledged the existence of two disagreements with Halo Studios and Microsoft. On the one hand, they are asked to do a job that they cannot continue doing for free due to their size, and on the other, they are not happy with the way in which Halo Studios manages the community.