A computer network firewall or network filter functions normally to pass data on open ports to a respective service or data source associated with an open port. In addition, traffic arriving on closed ports may be directed to a handler for analysis and response. The handler may analyze and catalog the source and type of traffic arriving on the closed ports. The handler may then send a response with either a fixed response or data tailored to the type and nature of the traffic. The handler may respond slowly to cause the source of the traffic to wait for the response, thereby slowing the speed at which a potential attacker can identify valid targets and proceed past non-valid targets.