A firewall, put simply, is a barrier – a barrier between a secure and trusted internal network and that of an outside network.
It is defined as a network security system which monitors and controls network traffic based on set security rules. A firewall can help block hackers or malicious software from infiltrating your computer through the internet or a network, as well as stopping your computer from sending malicious software to other computers.
Firewalls can be implemented in both hardware and software, or through a combination of both. Generally, there are two types of firewalls; a network firewall is a software appliance which runs on hardware which filters traffic between two or more networks, while a host-based firewall is a layer of software on one host that filters traffic on a single computer.
Firewalls date back to the late 1980s when the Internet was still new in terms of connectivity and usage. The first type of firewall was the packet filter, which were filter systems first developed by engineers from Digital Equipment Corporation.