Software installed in a user's computer that offers protection against unwanted intrusion and attacks coming from the Internet. Personal firewalls are available from numerous security vendors, and Windows XP includes its own (see Windows Firewall).|
For home and small business networks, a router with a built-in firewall is often used, and personal firewalls can be disabled, although they are often kept running as well. The central firewall provides easier administration than a firewall in each user's machine.
In an enterprise, a firewall is often a stand-alone appliance. In addition, a comprehensive security program may comprise several firewall functions in different venues, each providing a different level of protection. See firewall, software firewall and IDS.