STREAM RECOGNITION AND FILTERING

A method obtains a first data item signature for a first data item, the first data item signature comprising an association between a plurality of synch points in the first data item and a corresponding plurality of block signatures. The process attempts to find one of the plurality of synch points in a second data item; and, if such a synch point is found, then a block signature of a corresponding block of bits in the second data item is determined by applying a hash function to the corresponding block of bits in the second data item. The process ascertains whether the synch point and corresponding block signature from the second data item correspond to a synch point and block signature in the first data item signature. If a predetermined number of synch points and corresponding block signatures match, the first and second data items are considered to match.