1. A computer implemented method of automatically identifying a classified website comprising: on a server system having one or more processors and memory storing one or more programs for execution by the one or more processors: determining that a website is a candidate site; determining from among pages constituting the candidate site one or more listing page candidates; determining from among pages constituting the candidate site one or more detail page candidates; determining a listing page score using a listing page classifier, wherein the listing page score indicates a likelihood that the one or more listing page candidates are part of a classified website; determining a detail page score using a detail page classifier, wherein the detail page score indicates a likelihood that the one or more detail page candidates are part of a classified website; determining a candidate site score based in part on a combination of the listing page score and the detail page score; and determining that the candidate site is a classified website when the candidate site score is above a threshold.