6. The apparatus of claim 4 , the adult hub detection block further comprising: a preliminary adult document classifier block configured to classify a document as a preliminary adult document if the corresponding document score exceeds a first threshold; a preliminary adult group classifier block configured to classify a group as a preliminary adult group if the number of preliminary adult documents divided by a total number of documents in a document group exceeds a second threshold; a hub candidate classifier block configured to classify a candidate hub as an adult hub if the number of preliminary adult groups divided by a total number of document groups associated with the candidate hub exceeds a third threshold.
7. The apparatus of claim 6 , wherein crowd-sourcing is utilized to verify the classification of at least one candidate hub as an adult hub.