Hi, this is not exactly a question I would ask on a forum like this one, but nevertheless I will ask it. I had an argument with someone about firewalls and would like to collect some arguments supporting my view. The person I was talking to said that if you are not running services listening on given ports (say SMTP on port 25), you don't have to block these ports on your firewall. In other words, if your commuter did not have any services running, you would not need a firewall at all. I don't think that is true, but how do I suppor my view? My argumen was that if someone installed a virus listening on a port, say on port 25, my server could be vulnerable to an atttack. But the guy I was arguing with said, that it would have to be myself installing the virus - because viruses don't install "themselves" in Linux as they do in Windows. OK, but there must be other reasons to using firewalls, supporting my view. Are there any kind experienced network adminisrators out there who would like to give me some more examples showing why a firewall blocking a prot would be needed even if there was no service listening on that port?