A firewall is a barrier between your computer and others on the internet. Its purpose is to block attempts by malicious people to gain access to or destroy the information on your computer.
If you have broadband, it's especially important to have a firewall because your computer is permanently online, giving people (or their destructive or prying computer programs) plenty of time to try to attack it.
A firewall can consist of software – that is, a computer program – or hardware. A software firewall is the most important one to have. However, if your computer's operating system is Windows XP, Vista or 7, it will already have the built-in Windows firewall. And these days, most broadband routers incorporate a hardware firewall.
There is lots more advice on internet safety on the Get Safe Online website.
Fiona Syrett is a Digital Unite tutor.