Compares several "top-down" algorithms for identifying mirrored hosts on the Web. The algorithms operate on the basis of URL strings and linkage data: the type of information about Web pages easily available from Web proxies and crawlers. Results reveal that the best approach is a combination of five algorithms: on test data this approach achieved a precision of 0.57 for a recall of 0.86 considering 100,000 results. (Contains 19 references.) (Author/AEF)