Abstract: A data processing system has a searching mechanism for finding occurrences of a plurality of key strings within a target string. The searching mechanism forms a hash value from each of the key strings, and adds each key string to a collection of key strings having the same hash value. It then selects a plurality of symbol positions in the target string, and forms a hash value at each selected symbol position in the target string. This hash value is used to select one of the collections of key strings. Each key string in the selected collection of key strings is then compared with the target string.