Firewalls are security control points , allowing sites to safely connect trusted networks to untrusted networks. In the next chapter we will discuss how firewalls work and the role they play in internetwork security. Firewall Limitations Information-security professionals often find themselves working against misconceptions and popular opinions formed from incomplete data. Some of these opinions spring more from hope than fact, such as the misguided notion that all network-security problems can be solved simply by deploying a firewall. While firewalls deserve a high spot on the agenda for organizations that have, or are creating, a connection between their network and others, firewalls are not the whole answer.
Many threats remain outside the scope of a firewall's capabilities.
In fact, many of the hacking incidents reported by the media have very little to do with the Internet itself. Social engineering, one of the most widely used hacking techniques, involves tricking someone into revealing something that compromises security, such as a network password. Information-security surveys consistently report that more than half of all incidents are insider attacks, and many seasoned security professionals believe that insiders cause as many as 80 percent of all security problems. Viruses are self-replicating code that can cause considerable disruption on networks as well as on individual workstations. A Trojan horse program, such as a password sniffers, pretends to be something it is not to accomplish the aims of its creator.