A firewall, in its simplest form, is a barrier between the Internet and your computer. A firewall allows only the communication you want to reach your computer as illustrated in the drawing from HowStuffWorks.com.
The implementation of a firewall takes many forms in both hardware and software. One or both forms help protect your computer and your information from the “bad guys” lurking around the Internet. A firewall is used as part of the “Defense in Depth” approach the Information Technology community has begun to use for information security.UMKC Information Services uses both hardware and software firewalls as a major component of information security for UMKCnet and the university community.