The rapid updates of messages and users' information in social networks make it very difficult to efficiently identify unauthorized users and further hard to protect messages. Existing mechanisms for security protection usually have high overhead. In this paper, a multi-dimensional vector based access control model is used to solve these problems. Firstly, multi-dimensional vector for each user is constructed. Then based on a novel access control model proposed in this paper, the vector in

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... l networks is utilized to judge whether an access request is permitted. At last, we give some examples to verify our methods.