What is a firewall ?

A firewall is a system designed to prevent unauthorized acess to or from an internal private network. Firewalls can be implemented in hardware, software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet. All traffic entering or leaving the private network (or a particular PC) passes through the firewall, which examines and blocks traffic that does not meet some specified security criteria. Firewalls are a vital part of securing a system/network.