Abstract: An apparatus, system, and method for measuring the similarity of communication packet binary objects to classified object binary objects is disclosed. The method determines at least one pattern signature in an Nth binary object, accessing a location in a similarity store which has object identifiers for each of the previous N?1 binary objects which contain the corresponding pattern, and writing the object identifier of the Nth binary object at that same location in the similarity store. Reporting the number of locations in similarity store which contain the object identifiers of a communication packet and a classified object is a measure of similarity to each other. Outgoing packets are blocked if they correlate highly with confidential documents or objects.