Apart from understanding how firewalls function, it is also very important to recognize their limitations and to supplement them if necessary. For example, the firewall provides no protection against malicious content entering the local network on the permitted routes. Although it is true to say that the effects of some viruses and worms are reduced because they cannot communicate via the required ports, the firewall by itself does not provide real protection against viruses.
Similarly, the interception to confidential data on the Internet cannot be prevented by the firewall. Data that has passed the firewall and reached the insecure network is exposed to the known dangers there. Even when using a firewall, confidential information such as contracts, passwords, development information, etc., should therefore only be transferred with suitable protection, such as by using suitable encryption methods or via VPN connections.
