A method and apparatus is described for identifying content in a packet. The method may obtain data sample from the packet where the data sample is in a predetermined window at an initial offset point in the packet. For each offset point, a first stage of processing on the data sample may be performed to identify if the data sample corresponds to potentially relevant reference string. A more focused second stage of processing may then be carried out on the data sample to identify if the data sample corresponds to potentially relevant reference string. Thereafter, an even more focused third stage of processing may be carried out on the data sample to obtain a third stage result. If the data sample passes all three stages of processing, a predefined action is identified which is associated with a reference string corresponding to the data sample.