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Hacking the Hacker by Roger A. Grimes

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17Firewalls

Firewalls are a great example of technology being a victim of its own success. Firewalls have worked so well at defending computers for three decades that the threats they were created to prevent have almost stopped even being tried. The bad guys are giving up! At least on those types of threats. Some experts have even argued whether firewalls are even necessary anymore, but most believe that firewalls, like anti‐malware scanners, are an essential item in anyone’s computer security base configuration.

What Is a Firewall?

In a nutshell, a firewall is a software or hardware component designed to prevent unauthorized access between two or more security boundaries. It is traditionally accomplished by a protocol name or port number and usually at the network level using packet filtering. Many firewalls can also allow or deny traffic based on user names, device names, group membership, and information found in the upper levels of the application traffic. They often offer additional and advanced features such as high‐level packet analysis, intrusion detection/prevention, malware detection, and VPN services. Most firewalls come with detailed log files. Turning on any firewall will usually result in a log file full of entries.

The Early History of Firewalls

The beginning of what security experts would later identify as being an early application‐level firewall was created in 1987 by AT&T Bell Labs admins Dave Presotto and Howard Trickey on a VAX computer running BSD with ...

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