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Introduction to cyber security: stay safe online
Introduction to cyber security: stay safe online

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1.1 Personal firewalls

The startings of a brick wall.
Figure 2

Most operating systems come with a firewall that is installed as part of an operating system.

This firewall is only able to protect the computer it is installed on (and any devices attached to it) from an attack, so it is called a personal firewall. It is not intended to replace a network firewall which prevents attacks from outside of the network (such as from the internet).

Personal firewalls are especially useful for people with portable computers which will inevitably be connected to a wide range of computer networks. While we all hope and, to some extent, trust the people responsible for maintaining these networks to maintain a safe system, we cannot be sure that these networks are not compromised. The personal firewall on our own computers therefore adds a layer of protection between our personal data and a potentially untrustworthy (but useful) network.

Personal firewalls are the responsibility of individual computer users. If you have complete access to your computer’s settings then it is entirely possible to turn off the personal firewall and leave your computer vulnerable.

First of all, you can check your own computer to see how well protected it is at the moment. To do this you can visit a website designed to probe your computer to see what it can access and what is blocked. The site we are using is shieldsup [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] . Read the information on that page before proceeding.

  • Start with the instant UpnP Exposure test probe. The response you want to see is: THE EQUIPMENT AT THE TARGET IP ADDRESS DID NOT RESPOND TO OUR UPnP PROBES!
  • Next, the file sharing probe. The response you want is: Your Internet port 139 does not appear to exist! One or more ports on this system are operating in FULL STEALTH MODE! Unable to connect with NetBIOS to your computer. All attempts to get any information from your computer have FAILED.
  • Common ports: You want to see a green ‘Stealth’ for the status of all ports.
  • All service ports: you want to see a complete green ‘Stealth’ grid of all ports
  • Messenger spam: I have mine turned off.

In the next sections, you’ll learn how to check that your default personal firewall installed with your computer is running correctly. Once you have updated your firewall settings you can come back to shieldsup and see if the probes are now kept out.