I believe Dropbox create a hash for all users' files that point to a single file hosted on Dropbox, so Dropbox save the space that would have been occupied by t

I believe Dropbox create a hash for all users' files that point to a single file hosted on Dropbox, so Dropbox save the space that would have been occupied by the - according to them - redundant files. You could say that a Dropbox repo is like a list of references to non-redundant files hosted by Dropbox. In finding any disagreeable content, I believe the implication was that Dropbox could map it the other way around from the infracting file to a list of users with the file's hash.