We present an approach for secure information flow property preserving refinement and transformation of UML inspired interaction diagrams. The approach is formally underpinned by trace-semantics. The semantics is sufficiently expressive to distinguish underspecification from explicit nondeterminism. A running example is used to introduce the approach and to demonstrate that it is of practical value. Categories and Subject Descriptors K.6.5 [Management of Computing and Information Systems]: Security and Protection; D.2.1 [Software Engineering]: Requirements/Specifications General Terms Design, Languages, Security Keywords Model Driven Architecture, Information Flow Security, Refinement, Transformation, UML