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A system designed to
prevent unauthorized access to or from a private network.
Firewalls can be implemented in both hardware and software,
or a combination of both. Firewalls are frequently used to
prevent unauthorized Internet users from accessing private
networks connected to the Internet, especially intranets.
All messages entering or leaving the intranet pass through
the firewall, which examines each message and blocks those
that do not meet the specified security criteria.
There are several
types of firewall techniques:
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