The internet is effectively a public network, meaning that any connected device can find and connect to any other connected device. A firewall is a barrier between the internet and your computers or network – preventing unauthorised visits to or egress from your systems.

A firewall protects your organisation against:

  • Hackers breaking into your computer or network.
  • Worms – types of viruses that spread from device to device online.
  • Some outgoing traffic originating from a virus infection.

What a firewall does NOT do:

A firewall is not sufficient on its own to guarantee security, but constitutes the first line of defence. You also need to take the other protective steps outlined on this website. Remember that a firewall provides little or no protection against the following:

  • When you have granted permission for other computers to connect to yours.
  • When it switched off, disabled or contains many exceptions or open ports.
  • Most malware and spyware installations.
  • Spam.
  • Any kind of online fraud or criminal activity.
  • If you or a virus has created a ‘back door’ through the firewall.
  • People with physical access to your computer or network.
  • Data introduced to the computer other than online, for example via USB connected devices, CD/DVD etc.
  • Attacks after a network has been compromised.
  • Traffic that appears to be legitimate.

However, none of above constitute a reason NOT to install a firewall, as you should always assume that your ISP does NOT provide any kind of firewall.

Types of firewall

Personal firewalls

Personal firewalls should be installed on each computer that is connected to the internet and monitors (and blocks, where necessary) internet traffic. They are also sometimes known as ‘software firewalls’ or ‘desktop firewalls’.

Windows Firewall is a basic personal firewall. It is free, included with Windows operating systems. In Windows 8, Windows 7 and Vista, the Firewall defaults to active, so you need not worry about configuring it yourself.

If you wish, you could replace Windows Firewall with another personal firewall of your choice, including the type incorporated in some internet security packages, or standalone firewall software which can be downloaded from the internet, some of which is free of charge.

Hardware firewalls

Medium-sized and large businesses may need a hardware firewall – in addition to personal firewalls – depending on the configuration of your IT infrastructure. If in doubt, seek professional advice on selection installation and configuration of the most suitable one for your business needs.

Check if your Windows Firewall is switched on in your computer’s System and Security settings in the Control Panel


Jargon Buster

A Glossary of terms used in this article:


Universal Serial Bus: a means of physically connecting computers and peripherals such as external storage, keyboards and MP3 players.


The transmission of information over a network or the internet.


Unsolicited commercial e-mail. Also known as junk e-mail.


Internet Service Provider: a company that provides access to the internet.


Hardware or software designed to prevent unauthorised access to a computer or network over the internet.