Comment by jkp56

These hashes also reveal domain names. Most users visit many URLs on a small set of domains. If a user requests 1000 hashes that all can map to Reddit, it's very likely that the user is indeed reading Reddit. Another way to look at it: if the same person appears in a crowd on hundreds of photos, it's trivial to notice that there is something special about this person, even though in all cases the person was k-anonymous.