1. A method comprising: in response to a first query to which a search engine returns a first query result, comparing, at a server configured to receive the query results from a search engine, the first query result to multiple prior query results returned by the search engine in response to prior queries, to determine a similarity measure between the first query result and each of the multiple prior query results, wherein the comparing includes counting a number of identical result items included in both the first query result and in the each of the multiple prior query results, and determining the similarity measure for respective ones of the prior queries by computing a ratio between twice the number of identical result items and a sum count of total result items in the first query result and in respective ones of the multiple prior query results for the prior queries; identifying unique result items in one or more of the multiple prior query results for which the similarity measure exceeds a similarity threshold of 90% that are not included in the first query result; and combining the first query result and the unique result items as a combined search result responsive to the first query, wherein the combined search result excludes duplicates of any result that appears in the first query result and in any one of the multiple prior query results.