In this paper, we propose a dynamic audit service for verifying the integrity of untrusted and outsourced storage. Our audit service, constructed based on the techniques, fragment structure, random sampling and index-hash table, can support provable updates to outsourced data, and timely abnormal detection. In addition, we propose an efficient approach based on probabilistic query and periodic verification for improving the performance of audit services. Our experimental results not only

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... e the effectiveness of our approaches, but also show our audit system has a lower computation overhead, as well as a shorter extra storage for audit metedata.