So, I was watching the Halo Anniversary terminals today and noticed that when 343 guilty spark comes in contact with unknown sentients that crash land on installation 04 the timeline is 40,000 years before the events of Halo:CE. I believe the terminal is assault on the control room correct me if I am wrong but, there are a few terminals that cover the subject but, whatever. Anyway, when you see the crashed ship it first appears of covenant design, but if you look closely and pay attention to details on the ship you will notice green highlights and a few spike looking things coming of the back.
These observations have led me to believe that this will be either our enemy or a new type of species that will see in Halo 4 but, my guess is that they will be hostile and be our new main enemy. 40,000 years to me is ancient even with the forerunners becoming extinct 100,000 years ago.
This is the only direct evidence of what kind of enemy we may be seeing in Halo 4. Please, leave a comment and tell me what you think and please feel free to correct me on anything.