Security is a crucial aspect in any modern software system. To ensure security in the final product, security requirements must be considered in the entire software development process. We evaluate in this paper how security requirements can be integrated into the analysis phase of an object-oriented software development process. Our approach is model driven by providing models for security aspects related to the models for functional requirements. We investigate how the security models can be generated from the functional models. We give a graph-based formal semantics to the security models and present verification concepts which ensure the security requirments in the models. Categories and Subject Descriptors bla General Terms Design, Security, Verification Keywords Graph Transformations