A firewall is a computer security device which is configured to permit, deny or proxy data connections set and configured by the organization's security policy . Firewalls can either be hardware and/or software based.

A firewall's basic task is to control traffic between computer networks with different zones of trust. Typical examples are the Internet which is a zone with no trust and an internal network which is (and should be) a zone with high trust. The ultimate goal is to provide controlled interfaces between zones of differing trust levels through the enforcement of a security policy and connectivity model based on the least privilege principle and separation of duties .

Without an operating firewall on your computer or network anyone will be able to infultrate your system and take control or moniter your activity.