Let’s put your firewall to the test

Fred langa By Fred Langa

Most PC users take it on wary faith that their firewalls are providing full protection from malicious applications.

A better policy is to use firewall testing services and free applications to ensure your firewall is correctly set.

Get free testing with online services

Brian Brooks wants to make sure his firewall/router is doing its job.
  • “The other day, while using my Netgear DG834 modem/router, I was wondering whether there are any good tools that can safely test a firewall setup from the outside. I vaguely remember years ago reading about tools that will check ports, etc. I would really find it useful if you’d recommend a few basic checks.”
The best place to start is Steve Gibson’s free and reliable Shields Up firewall testing site.

A PC’s Internet “ports” are numeric addresses that online sites use to communicate with your PC. Shields Up rapidly and safely checks your ports and reports on the status of each one as follows:

  • Open — available for use by anyone on the Internet (and potentially, a hacker’s doorway to your PC)
  • Closed — unavailable to outsiders but still visible to anyone searching for open ports on the Internet (inviting further attacks from hackers)
  • Stealth — closed and completely invisible to outsiders
Another highly regarded and free port probe is on HackerWatch’s site.

It’s smart to use more than one port probe. While one test might miss something, it’s much less likely that two independent tests will.

After testing a firewall from the outside, test it from the inside with leak tests. Mimicking malware, these tests safely and harmlessly try to phone home to a test site. Properly configured firewalls will warn you when an app tries to contact an online site, giving you the option to cut the link.

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All Windows Secrets articles posted on 2010-03-11:

Fred Langa

About Fred Langa

Fred Langa is senior editor. His LangaList Newsletter merged with Windows Secrets on Nov. 16, 2006. Prior to that, Fred was editor of Byte Magazine (1987 to 1991) and editorial director of CMP Media (1991 to 1996), overseeing Windows Magazine and others.