Abstract: An improved partial packet filter (10) for filtering data packets (210) in a computer network (12) wherein a candidate field (413) of the data packet (210) is hashed to a plurality of bit-wise subsets (636) each being an independent representation of the candidate field (413). Each of the bit-wise subsets (636) is compared to a reference hash table (644) which has been prepared in a preliminary operation series (514). The preliminary operation series (512) configures a plurality of target fields (714) to set selected memory locations (312) in the reference hash table (644).