Over the past years, research on specifying, designing and developing secured information systèmes (IS) has been very active. Some contributions have focused on integrating security aspects, mainly access control mechanisms, at the implementation phase. Others pay a particular attention to the capture and analysis of security requirements. However, to our knowledge, no method addresses the whole problem of the specification of security requirements and their transformation through all the phases of the IS development life cycle. We argue that better Secure IS can be obtained if security issues are taken into account at an earlier phase of the system life cycle and integrated with functional aspects along the whole life cycle. This paper is a step forward to a comprehensive security conceptual meta-model encompassing the main security properties such as availability, integrity, confidentiality, and accountability. It integrates functional and non-functional requirements. It includes socials, organizational as well as informational aspects. This meta-model is the backbone of our approach.