11. The method of claim 1 wherein the set of documents of known classification comprises a set of spam e-mails such that receiving, at the duplicate detector, a set of documents of known classification comprises receiving, at the duplicate detector, a set of spam e-mails.
11. The method of claim 1 wherein the set of documents of known classification comprises a set of spam e-mails such that receiving, at the duplicate detector, a set of documents of known classification comprises receiving, at the duplicate detector, a set of spam e-mails. 12. The method of claim 11 wherein calculating, at the duplicate detector, class signatures based on the set of documents of known classification and the lexicon of attributes comprises calculating spam signatures based on the spam e-mails and the lexicon of attributes.