Abstract: A data processor is connected to a digital communication system such that information packets broadcast on the system are examined to determine if the contents of each packet meet selection criteria, whereupon the packet is coupled to the processor. A state machine or interface processor is connected between the processor and the network, and compares packets to the selection criteria, passing accepted packets and blocking rejected ones. The selection criteria are programmed into the state machine as a decision tree of any length, configuration or data requirements, preferably by the attached data processor, and can include examination of arbitrary sections of the packet for equality/inequality, greater-than/less than, signed and unsigned comparisons and bit mask comparisons. Thus content is variably examined, as opposed to checking for an address or key code at a given byte position. The state machine operates on recognition instructions including byte offset and content specifics.