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Firewalls monitor data coming in and out of networks and leverage pre-established rules and filters to keep systems protected from unauthorized access. They protect against the growing number of thieves and criminals who steal data, hold systems hostage, and use malware to take control over computers and systems.

Firewall technology has grown and evolved since its introduction in the late 1980’s, and today, there are several different types of firewalls that offer a range of protection. Network-based firewalls guard entire networks and are typically hardware, while host-based firewalls are software applications that protect individual devices, called hosts, on a network.

Packet-filtering firewalls examine each data packet in isolation without knowing the context of a connection; stateful inspection firewalls examine packets in a more contextual manner, and circuit-level gateways monitor TCP handshaking between two connections (clients or servers) to prevent unauthorized access by examining the information contained within the handshake. Application gateway firewalls, also known as proxy firewalls, examine traffic at the application layer of the OSI model and provide additional security by allowing or denying traffic to specific services based on established policies.

A unified threat management firewall combines the functions of a SMLI firewall with intrusion prevention and antivirus, and is offered as software that is installed on a system. It is important to remember that firewalls require regular updates in order to remain effective against the latest security threats. A change management plan is important to ensure that all firewall updates are implemented in a timely manner.