Not all security risks stem from the compromise of software and credentials. Many security risks commonly referred to as Denial of Service, or DoS, attacks, affect the quality of service offered by a computer system, and can be just as damaging as a system compromise. If your firewall is down and you cannot send email to a customer to confirm a business deal, the loss of revenue could be greater than if your firewall were compromised and the intruder knew about the deal.

It is extremely important for the security of our systems to ensure that the hardware they run on is adequate, and therefore performance monitoring, as mentioned duringChapter 5, should be carried out regularly, and unusual activity, such as high network or CPU usage, should be accounted for. Such administration forms an important part of making sure that our firewall is not only secured against simple attacks, but is also resilient both against DoS attacks and surges in usage.

If one performance...