This work presents a number of Models for the Evaluation of Firewall Systems. The culmination of which is a generalized model which is used to evaluate firewall systems in a complex computing and network environment. The whole idea of the model is to provide a single value which sums all the security characteristics of the firewall and assess its ability to secure a particular environment as defined by the user. The fact that the user is able to define the inputs to the model makes the model dynamic. It is of interest to note that the model which we call the Firewall Vulnerability Assessment Confidential Parameter (FVACP) communicates exactly which firewall to choose in one s given environment. It is now easy for any company to select a firewall which suits its security needs and be able to make computer security strategic decisions. The fact that the FVACP is a general model means that it is a starting point in computer security metrics.As system engineers follow it a number of times they will be able to develop their own variations of the model depending on their situation. This research presence deep theoretical insight on a complex subject of metrics