The human race has evolved and thrived despite perpetually being attacked by different kinds of viruses, infections, diseases, etc. The body?s natural immune system and self healing mechanism as well as the assisted healing systems in human communities has played a major role in this accomplishment. This model has served as an inspiration for the development of a new paradigm for security that we have proposed in this paper. While most security systems focus on defense of a single machine or a cluster of machines we have taken a radically different approach to security. We look at defense of functionalities rather than systems in the traditional sense. In this paper, we propose a new way to look at security called the functionality (such as e-mail server, web services server, etc) defense by heterogeneity. Further we present an analysis, architecture and an algorithm for defending functionality.