Automated attack tools are always seeking ways to break into and take over your system. Severe attacks may delete important data, crash your system, spawn new attacks, or even steal personal information, such as passwords and credit card numbers. A firewall can help protect your computer by blocking potentially hostile connection attempts. Unit firewalls (firewalls that are designed to help protect multiple computers in a university department, or a home or apartment complex network) and properly configured personal firewalls (firewalls that you can install on your own computer) can each provide effective security to suit various needs. For home use, personal firewalls are often free.
Learn how to set up a firewall:
Important: Windows XP and Mac OS X have built-in firewalls. It is important to ensure your firewall is enabled for complete protection. Many Linux or other UNIX-based systems also have firewall or filtering capabilities that should be enabled.