Abstract: A binary state machine system and method for REGEX processing of a data stream in an intrusion detection system are disclosed. The method comprises maintaining a state table. The state table is indexed such that inputs comprising a current state and a current character yield an output of a new state. The new state is related to an indication of an attack on a computer network. The method further includes maintaining the current state. An input stream comprising a plurality of characters is received. A first character of the input stream is selected as the current character. The current character and the current state are compared to the state table to generate a new state.