Interesting listener.ora / listener password and VMS error
TNS-12570
TNS-12560
TNS-00530
He says the issue is becuase they are using something called host naming to connect to the database and they have a blank listener.ora file. A quick check on Google failed to find a solution to the issue but I did find a very nice paper called "Security best practice: Host Naming and URL conventions" written by Gunter Ollmann. If anyone has any ideas to solve taupirho's problem please log onto my Oracle security forum and let him know.