16. A non-transitory computer storage medium storing instructions, the instructions comprising: one or more instructions which, when executed by one or more processors, cause the one or more processors to identify a plurality of documents; one or more instructions which, when executed by the one or more processors, cause the one or more processors to expand the identified plurality of documents to generate an expanded plurality of documents, where the expanded plurality of documents includes an entirety of documents in the identified plurality of documents and one or more additional documents, and where each additional document, of the one or more additional documents, links to a document in the identified plurality of documents or is linked to by a document in the identified plurality of documents; one or more instructions which, when executed by the one or more processors, cause the one or more processors to determine a similarity measure for each pair of documents in the expanded plurality of documents, where, for a pair of documents, in the expanded plurality of documents, that includes a first document and a second document, the similarity measure is determined based on: whether the first document contains a forward link to the second document, whether the second document contains a forward link to the first document, and a quantity of documents, in the expanded plurality of documents, that contain both a forward link to the first document and a forward link to the second document; and one or more instructions which, when executed by the one or more processors, cause the one or more processors to group, based on the similarity measures, documents, included in the expanded plurality of documents, into clusters to form clustered documents.
19. The non-transitory computer storage medium of claim 16 , where documents, included in the expanded plurality of documents, include web documents, and where the forward links include hyperlinks.