Thank you very much for your help. I will now contact the person in charge of the local network and explain exactly what you have told me. I had already reported this attack but they were unable to solve the problem...
If this doesn't work I will try to block these ping broadcasts at the local Unix/Linux machines like Michael Stone sugested. Anyway, this list has won another subscriber and I will do my best to learn as much as I can about Linux security so that I can also be of some help to others. Nuno Faria
