Firewalls are essential devices or programs that help organizations protect their networks and systems, and help home users protect their computers, from hostile attacks, break-ins, viruses, and malicious software. Firewalls control the flow of network traffic between networks and between hosts that... See full abstract

Firewalls are essential devices or programs that help organizations protect their networks and systems, and help home users protect their computers, from hostile attacks, break-ins, viruses, and malicious software. Firewalls control the flow of network traffic between networks and between hosts that employ different security policies. Firewalls were originally installed at the perimeter of networks, where hostile threats from external intruders could be detected and stopped. While these early firewalls provided some protection for an organization s internal systems, they could not recognize all instances and all forms of attack. For example, attacks sent from one internal host to another often did not pass through the network firewalls, and viruses and malicious code could not be detected. Networks can now be designed to provide protection at the network perimeter as well as at other network locations and to detect both external and internal attacks. Firewalls can now be used to restrict connectivity to and from internal networks that process personal information and carry out sensitive functions, such as accounting and personnel tasks. Firewalls can provide an additional layer of security by preventing unauthorized access to systems and information, and they can protect mobile devices that are placed directly onto external networks. To help organizations use today s firewall technology effectively, the National Institute of Standards and Technology (NIST) recently revised its guide to firewall technology and the development of firewall policies.
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