Dear All, I have recently discovered a problem with my firewall service. It blocks all network traffic on the external interface, using 60-100% of the CPU. If I stop the service, everything returns to normal (processor and network traffic), and when I restart it the problem appears again. I have Win2K Server with SP3, ISA server with SP1, no SQL, Exchange and a virus scan comes up negative. Nothing has changed in weeks and this has started happening! There are no indications of port scan/hack/anything weird happening, and Technet online tells me to install SP1. Can anyone give me any further information on the problem :) ...Spence