A system used to protect corporations, small businesses and home PC private networks from attacks by viruses, worms, spyware, and hijacks. All messages going into and out of a private network must pass through the Firewall which is setup to block those messages that do not meet certain specified security criteria. Firewalls are considered the first line of defense preventing unauthorized users from accessing private networks. Firewalls have long been in place in large, multi-user companies. Because of the surge in email and internet threats, more and more small business and home systems are set up with Firewall protection.

According to the Internet Storm Center, an unprotected PC will normally come under attack within 20 minutes of being connected to the Internet.