The Internet has made large amounts of information available to the average computer user at home, in business and in education. For many people, having access to this information is no longer just an advantage, it is essential. Yet connecting a private network to the Internet can expose critical or confidential data to malicious attack from anywhere in the world. Users who connect their computers to the Internet must be aware of these dangers, their implications and how to protect their data and their critical systems. Firewalls can protect both individual computers and corporate networks from hostile intrusion from the Internet, but must be understood to be used correctly.