You might be infected with the W32.Nachi virus, a stealthy bandwidth-killing worm that goes undetected by most virus-scanners, including the latest updated version of Norton 2003 Pro. If you have strange bandwidth issues as if you're being pinged, it could be that you or one of the computers you're routed with may be infected. Download Network Associates Stinger, a program (or worm) specially designed to deal with worms such as this. :)