A firewall is a program or device that is used to control access to a computer or network. It sits between a restricted system and the Internet, so all traffic in or out must flow through it.
Firewalls work like security guards to protect a computer. The firewall uses policies set by the firewall’s user to determine whether to allow the computer to access sites or other computers on the Internet.
A policy might specify things like:
Allow information to come into the computer from web sites, but not from a game server.
Block all communications from certain sites that have caused problems.
If a person using the computer requested something from the outside computer, allow that computer to respond.
Certain computers can send information only to a web browser, but not to other programs.
Don’t allow programs on the computer to send out information unless the user has approved it.
If a computer has no firewall, nothing is controlling who and what can enter and leave. When you connect a computer to a network, including the Internet, your system can be a target. Some things that can happen include:
- Exposing information from your computer to others.
- Allowing resources, such as disk space, to be used by an attacker.
- Causing your system to be unusable.
Firewalls can help prevent attacks from getting through and harming your computer.
The Interhack company of Ohio provides excellent information about firewalls with this series of Frequently Asked Questions.
The Carnegie Mellon Software Engineering Institute provides a thorough discussion about deploying firewalls.
For additional information on firewall software, read up on firewall software reviews.