DETECTING MIRRORS ON THE WEB

A system obtains multiple signals associated with first and second hostnames or subtrees. The system uses the multiple signals to determine whether the first hostname or subtree is a mirror of the second hostname or subtree. The multiple signals may include, for example, a same link structure and/or sitemap for the first and second hostnames or subtrees, duplicate content associated with the first and second hostnames or subtrees, a same Internet Protocol (IP) address or subnet for the first and second hostnames or subtrees, a same owner for the first and second hostnames or subtrees, nearly duplicate content associated with the first and second hostnames or subtrees, similarity between the hostnames of the first and second hostnames or subtrees; and/or an indication that one hostname or subtree of the first and second hostnames or subtrees redirects to the other hostname or subtree.