A port scan will test your IP or range of IP addresses for services that are listening on TCP ports and are open to public facing IP addresses. This provides an easy way to quickly test a firewall.

Entering an IP address or range of IP addresses into the form will have those targets scanned by one of our external servers. For this reason you must enter a public IP address that is routable from an external perspective and one that you have permission to scan. The results will be emailed to you once the scan has completed.

It is possible though highly unlikely that port scanning could cause listening services to become unstable.

Enter the target IP in either of the following formats:

192.168.1.5
192.168.1.1-20
* To scan a range of IP addresses you must have a valid membership with HackerTarget.com

The following is a sample nmap scan report

Starting Nmap 5.00 ( http://nmap.org ) at 2009-07-16 23:12 UTC
Interesting ports on lvps87-230-87-158.dedicated.hosteurope.de (87.230.87.158):
Not shown: 997 filtered ports
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 4.2p1 Debian 7ubuntu3.2 (protocol 2.0)
80/tcp open http Apache httpd 2.0.55 ((Ubuntu) mod_python/3.1.4 Python/2.4.3 PHP/5.1.2 mod_ssl/2.0.55 OpenSSL/0.9.8a mod_perl/2.0.2 Perl/v5.8.7)
8443/tcp open ssl/http Apache httpd 2.0.46 ((Red Hat) mod_ssl/2.0.46 OpenSSL/0.9.7a)
Service Info: OS: Linux

Service detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 64.27 seconds

We have scanned the IP Address: test.acunetix.com