1. In a network carrying a plurality of packets over at least one network link, the network including a first network component having memory and a processor and configured to store information in the memory about at least one of the plurality of packets, a method for detecting a target packet comprising: receiving at least one of the plurality of packets over the link to obtain a received packet; determining a representation of at least a portion of the received packet; identifying a location in the memory; associating a value with the location in the memory; receiving a query message identifying a target packet at the first network component; the first network component using the value associated with the location in the memory in processing the query message to determine if the target packet has been encountered; creating a reply if the target packet has been encountered; and the first network component making the reply available to the network if the target packet has been encountered; wherein the reply is capable of being used as part of a method for locating an intrusion point of the target packet in the network.