The year 2011 has witnessed a lot of high profiles data breaches despite the availability of IS security and governance controls, frameworks, standards and models for organisations to choose from; and the technical advances made in intrusion prevention and detection. Taking this issue into account the objective of this paper is to identify and analyse the weaknesses in the IS security defences of organisations from a holistic perspective, and propose a dynamic IS security governance process model for the implementation of appropriate controls and mechanisms for optimised IS security. Optimization is achieved through the strategic overlap of security and governance frameworks implemented in a prioritized phased manner for efficiency and effectiveness in cost, time and effort. The paper starts with the analysis of data breaches to identify the weaknesses in the organisational information system. This is followed by the analysis of recommended requirements and dimensions of effective IS security architecture, IS governance, concepts and models to identify relevant frameworks used in IS security and governance. Thereafter, the best practices for implementing the model is evaluated and finally the frameworks and IS entities are integrated into an optimized Information Systems Security and Governance (ISSG) process model.