In virtual reality systems which are collaborative and dynamic, i.e. where at run-time mutually interactive objects can be added or removed in different contexts and where their behavior can be modified, the problem of data security and privacy protection is renewed. In such virtual worlds operations on objects should or should not be allowed to users playing particular roles with respect to inter-object interactions. In this paper a method called VR-PR is presented, where privileges are represented by pairs: object - semantic operations induced from object interactions. Semantic operations are generated using automatic analysis of the object method call graphs. Then they are used in the privilege creation and modification process. Privileges based on semantic operations are expressive, flexible and consistent with permanently evolving set of objects composing the virtual world, interactions between the objects, and a set of users.