1. A computer-implemented method, implemented by hardware in combination with software, the method comprising, at least in part on a particular device in a network: (A) obtaining a first data stream signature for a first data stream, the first data stream signature comprising an association between a plurality of synch points in the first data stream and a corresponding plurality of block signatures, and associating at least one action with said first data stream, wherein said association comprises an ordered sequence of corresponding synch point and block signature pairs, and wherein, for a particular pair comprising a particular synch point and a particular block signature, the particular block signature associated with the particular synch point was determined by applying a hash function or message digest function to a corresponding particular block of bits associated with the particular synch point, and wherein said data stream signature is based on fewer than all of the bits in the data stream; (B) attempting to find a synch point of the plurality of synch points in a second data stream; and (C) if a synch point of the plurality of synch points is found in the second data stream, then: (C)(1) determining a block signature of a corresponding block of bits in the second data stream, wherein the block signature is determined by applying a hash function or message digest function to the corresponding block of bits in the second data stream; and (C)(2) ascertaining whether or not the synch point and the corresponding block signature from the second data stream correspond to a synch point and block signature in the first data stream signature; and (C)(3) when the synch point and the corresponding block signature from the second data stream correspond to a synch point and block signature in the first data stream signature, maintaining information indicative of the correspondence; (D) repeating steps (B) and (C) while at least some of the second data stream remains unprocessed, until a predetermined number of synch points and corresponding block signatures from the second data stream match synch points and corresponding block signatures in the first data stream signature; (E) determining a match between the first data stream and the second data stream when the predetermined number of synch points and corresponding block signatures from the second data stream match synch points and corresponding block signatures in the first data stream signature; and (F) in response to said determining a match in (E), performing one or more actions of said at least one action associated with the first data stream.