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This paper describes the attacks on a secure group communication with hierarchical access control, which arises in the communication group involving users with different privilege levels. The basic idea is to enable each subgroup to read the messages of those subgroups that are located at a lower level in the hierarchy. For such a setting, the Chinese remainder theorem based hierarchical access control scheme CRTHACS is proposed, which also aims at hiding the underlying hierarchy. Here we describe practical attacks, which allow for revealing at least parts of the hierarchy.