A system comprising a network resource server or a server farm formed by a plurality of computer systems and a network processor which transfers data exchanged with an external network supported by the server farm at a data rate substantially the same as the data flow rate of the network and related method. The network processor protects the network resource server against attacks such as a denial of service attack by monitoring data flow, computing a derivative of the data flow over time to determine the rate of change of data flow, and modifying instructions for the discarding of packets in response to rates of change which are outside predetermined boundaries.