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I've just tested my computer with Gibson's port scan test:

enter image description here

The test results stated that my system is "uncommon". It also said that my computer deliberately chose not to return. But I did not do any settings with my computer so I was wondering what is the reason that the probing tests had passed?

Or rather, what settings do I have to do to my computer to allow the probing tests to fail?

Windows Vista Home Premium sp2

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up vote 5 down vote accepted

According to ye olde standards, a computer would respond to every connection attempt with, typically, one of three responses:

  1. Application banner indicating that a service is listening and which service
  2. ICMP Port Unreachable - indicates that nothing is exists on this port
  3. ICMP Administratively Prohibited - indicates that your system is not allowed to access this port

By those rules of etiquette, one would expect firewalls to respond with the 3rd kind of message. However, nowadays one typically expects firewalls to drop packets without sending a response. This is what Gibson is referring to as "stealth mode".

Unfortunately, the Shield's Up website is fairly dated. The advice and analysis makes assumptions based on the late 1990's Internet. At that time it may have been a reasonable assessment, these days I wouldn't give it much credence.

A host based firewall has been included and enabled since Windows XP SP2. So, whether you realize it or not, you do have a firewall running. However, the more likely culprit is your home router. Those require special configuration, called port forwarding, to pass unsolicited traffic from the Internet to your computer.

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Port 139 could be dropped anywhere along the route from the Gibson scanner

  • ISP - Because NetBIOS is a local protocol, and not intended for the Internet, more and more ISP's are dropping this by default.
  • Your router - it may have a firewall built in
  • your computer - although you say you have disabled firewall, you may actually have NetBIOS turned off - check in your network properties

Unfortunately I think the comment from Gibson's software is misleading. It may have been true at some point that port 139 was common on the internet, but it is much less common now. I also wouldn't take any comfort from the comment that "this computer appears VERY SECURE" :-)

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Most likely your software or hardware firewall is "hiding" those ports by default.

The firewall prevents/filters responses to connecting attempts on those ports. That way attackers won't get information that help to fingerprint systems or misuse vulnerabilities.

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running netstat -an will show the open ports on the local machine (along with the connected ports) – symcbean Oct 14 '11 at 11:05
@Pekka this is weird, because I have no firewall / antivirus installed. windows firewall and defender are disabled as well – Pacerier Oct 14 '11 at 11:59
@symcbean heys how do i determine what ports are opened: – Pacerier Oct 17 '11 at 4:39

Gibson's scanner is outdated and not a good source of information on computer security. I would ignore the message as a relic of ancient history.

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so the site's a joke now? – Pacerier Oct 15 '11 at 12:14
@Pacerier: It's perfectly good for what it is, which is an online port scanner. It's just that the security landscape has changed over the last decade, perhaps in part precisely due to sites like ShieldsUP! raising awareness about the importance of good firewalls. In 2001, very few computers or routers would pass the full ShieldsUP! test out of the box; these days, if they don't, you have serious cause to complain. – Ilmari Karonen Oct 16 '11 at 15:25
@Pacerier - Gibson has, for a long time, been seen as a joke by many people. SpinRite was a good product, but even that was only true years ago. – DanBeale Oct 16 '11 at 22:03

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