Abstract: This paper discusses how object orientation in application design enables confidentiality aspects to be handled more easily than in conventional approaches. The idea, based on object fragmentation at design time, is to reduce processing in confidential objects; the more non confidential objects can be produced at design-time, the more application objects can be processed on untrusted shared computers. Still confidential objects must be processed on non shared trusted workstations. Rules and limits of object fragmentation are discussed together with some criteria evaluating trade-offs between fragmentation and performance.