At the basic level, a firewall protects a computer (or an entire network) from unauthorised traffic. It stops hackers breaking in, and stops sensitive data leaking out. Whilst almost always residing at the perimeter between your business and the internet there is also one built into every Windows computer.

Similar to immigration control at the Airport, a firewall sits at the border and inspects all network traffic coming in or going out. Rules then decide whether or not it may pass through to its intended destination, such as inbound email to the email server, web browsing out to the internet etc, the idea being that everything that is authorised may pass through, but nothing else. A Windows computer placed onto the internet without being protected by a firewall will be infected with a virus within seconds.

Remember that not all firewalls are created equally. Although they all perform the same basic tasks, the functionality and costs associated varies greatly. With the continually evolving landscape of cyber security threats, a firewall is critical in mitigating risk. You should review its configuration and capabilities regularly.