A method and apparatus for detecting predefined signatures in packet payload is disclosed. In one embodiment, a method of string matching in a network packet payload includes performing hash on a current search string received in the network packet payload to generate respective search string hash values, storing the search string hash values in a hash buffer, performing rehash using the search string hash values to generate an associated search string rehashed value, performing a parallel search of the search string rehashed value against Content Addressable Memory (CAM) entries to determine if the search string rehashed value matches with one of the CAM entries, and identifying the current search string in the network packet payload as a match with one of the CAM entries based on the outcome of performing the parallel search.