While Cloud data services are a growing successful business and computing paradigm, data privacy and security are major concerns. One critical problem is to ensure that data owners' policies are honored, regardless of where the data is physically stored and how often it is accessed, and modified. This scenario calls for an important requirement to be satisfied. Data should be managed in accordance to owners' preferences, Cloud providers service agreements, and the local regulations that may apply. In this work we propose innovative policy enforcement techniques for adaptive sharing of users' outsourced data. We introduce the notion of autonomous security-aware objects, that by means of object-oriented programming techniques, encapsulate sensitive resources and assure their protection. Our evaluation demonstrates that our approach is effective.