The Black Files, also known as the List, was a series of electronically encoded information that covered the atrocities committed by Khan Noonien Singh in an alternate timeline where the Augments won the Eugenics Wars.
The List was smuggled off Earth before the end of the wars by a group of Human colonists who managed to flee the planet on a sleeper ship called the Botany Bay. The Files were secretly placed within the vessel in order to prevent followers of Khan from destroying them, and it was hoped that the Augments would destroy one another, after which the surviving colonists would show their descendants the history of their planet and what brought it to ruin.
The existence of the Black Files was known to Khan and he placed a high directive within the Children of Khan to seize it through any means necessary. This was because a majority of Khan's actions had been rewritten by the Augments to make Khan seem as a benevolent warrior-noble and omitted the atrocities he committed in his life. In order to maintain this image, only a small cadre of Augments were known to know the truth of the matter and sought to make sure that the Black Files were never known to the rest of the quadrant. (Myriad Universes - Infinity's Prism novel: Seeds of Dissent)