9. Firewalls

A firewall is a program or hardware device that filters the data packets coming through the internet connection into your personal computer or into a company's network.

It is set up to allow mainly one way access, i.e. you can go out onto the internet and access pages, but it checks everything coming back against a set of rules. If the data coming back is from an unauthorised source, then it is blocked.

You may have heard people saying, 'I can't get on that site at school because it's been blocked'; that is the firewall in action.

Firewalls can also protect your system from hackers who might try to 'break-in' and access or steal data.

All networks and indeed all home PCs should have an active firewall.