1. A search engine apparatus for responding to a search query, the search engine apparatus comprising: 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 the candidate document, 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 score; and a filter block configured to remove any candidate document classified as adult from responses to the search query.