Abstract. This paper addresses the issue of confidentiality and declassification for global computing in a language-based security perspective. The purpose is to deal with new forms of security leaks, which we call migration leaks, introduced by code mobility. We present a generalization of the non-disclosure policy [AB05] to networks, and a type and effect system for enforcing it. We consider an imperative higher-order lambdacalculus with concurrent threads and a flow declaration construct, enriched with a notion of domain and a standard migration primitive.