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Re: Hidden Ports
From: Vincent <pros-n-cons () bak rr com>
Date: Tue, 3 Feb 2004 20:11:48 -0800

On Tue, 03 Feb 2004 15:46:12 -0200
Eduardo Sorensen <ovo () osite com br> wrote:

Can a port scanner not see a port that is opened?

The question is: can a backdoor be on a machine, and with nmap -p 1-,
for example, you couldn't see it?

Thank you,

What if the backdoor is set to ignore any address queries other than the owners?
For instance I run a mail server at home but even though I do not have a firewall
you will not see any service there unless you're on if you try scanning
from the service will not respond.
nmap -sV -p25
Starting nmap 3.48 ( http://www.insecure.org/nmap/ ) at 2004-02-03 20:05 PST
Interesting ports on hatch.localdomain (
25/tcp open  smtp    Sendmail 8.11.8/8.11.12
nmap -sV -p25
Starting nmap 3.48 ( http://www.insecure.org/nmap/ ) at 2004-02-03 20:08 PST
Interesting ports on nowhere.nex.com (
25/tcp closed smtp

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