A security flaw in patches from game developer Naughty Dog gave hackers access to unreleased content from The Last of Us Part II that was stored in an Amazon S3 bucket. The leak came from an unknown group, although speculation at the time had it that a disgruntled former employee was behind this action. Sony Interactive Entertainment (SIE) says that they identified the main individuals that released TLoUU2 assets and that they are note affiliated with Naughty Dogs or SIE. It appears that the Uncharted 3 server included some material from the initial release, so it was likely that content from upcoming release may also be present.
Source: https://www.bleepingcomputer.com/news/security/game-patch-gives-hackers-access-to-development-content-on-amazon-s3/