An improved technique employs an automated agent inside the network perimeter, which generates and sends data packets to a listener outside the network perimeter. Along these lines, the automated agent generates data packets over a specified range of security parameters including port number, payload format, and communications protocol. The agent attempts to send these data packets across the network boundary through a firewall at an egress or other point of the network. The listener receives the data packets and analyzes the payload content of each received data packet for each value of the security parameters (e.g., port number, file type, and protocol). The listener then sends the results of the analysis to a report generator, which summarizes the analysis for an administrator of the network.