Abstract. Language-based information-flow security is concerned with specifying and enforcing security policies for information flow via language constructs. Although much progress has been made on understanding information flow in object-oriented programs, the impact of class initialization on information flow has been so far largely unexplored. This paper turns the spotlight on security implications of class initialization. We discuss the subtleties of information propagation when classes are initialized and propose a formalization that illustrates how to track information flow in presence of class initialization by a type-andeffect system for a simple language. We show how to extend the formalization to a language with exception handling.