1. A search engine apparatus for generating a plurality of responses to a search query submitted to an online search engine, the search engine apparatus comprising computer hardware for executing: an adult hub detection block configured to calculate a hub score for an adult hub, wherein the adult hub is connected to a plurality of documents; a classifier block comprising a candidate document feature block configured to calculate a document score for a candidate document, the document score comprising a hub distance score measuring a hop distance between the candidate document and the adult hub, the hop distance corresponding to a total number of hops between the candidate document and the adult hub, and each hop corresponding to a direct connection between two Web documents, the classifier block configured to classify the candidate document as adult based on inputs comprising the document score of the candidate document and the hub distance score; a filter block configured to remove any candidate document classified as adult from the plurality of responses to the search query; a document feature block configured to calculate a document-level score for each of a plurality of documents in the network, said plurality of documents comprising at least one document connected to the candidate document in the network; and a synthetic feature block configured to calculate at least one synthetic score for each of a plurality of document groups associated with the plurality of documents in the network, each synthetic score comprising an aggregation of a plurality of document scores; the classifier block further configured to classify the candidate document as adult based on inputs comprising each of the at least one synthetic score.