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Abstract:The term "cloud computing" has been mentioned for just under two years in relation to services or infrastructural resources, which can be contracted over a network. Cloud computing is a flexible, cost-effective, and proven delivery platform for providing business or consumer it services over the internet. However, cloud computing presents an added level of risk because essential services are often outsourced to a third party, which makes it harder to maintain data security and privacy, support data, service availability and demonstrate compliance. we analyze many technologies, it also inherits their security issues identifying the main vulnerabilities in this kind of systems and the most important threats found in the literature related to cloud computing and its environment as well as to identify and relate vulnerabilities and threats with possible solutions. Cloud computing is surrounded by many security issues like securing data, and examining the utilization of cloud by the cloud computing vendors. Cloud computing has brought lots of security challenges for the consumers and service providers. The study aims to identify the most vulnerable security threats in cloud computing, which will enable both end users and vendors to know about the key security threats associated with cloud computing. It will enable researchers and security professionals to know about users, vendors concerns and also to critical analysis about the different security models and tools proposed.

Most of the protocols and algorithms used in MANET, are assuming that all mobile nodes cooperate fully with the functionalities of the network. But some nodes are cooperate partially or not at all cooperating. Network performance and data accessibility, accessing time, query delay are affected by these selfish nodes. The discussion of this paper is about, representing a Replica server which solves the selfishness. The Replica server monitors and maintains the status of all mobile nodes in the network. If it finds any selfish node in the shortest path between source and destination, the replica server will analyze the reason for selfishness and it finds solution. The conducted simulations demonstrate the proposed approach based on proxy method which outperforms in terms of network parameters such as accessing data, time and cost and also it improves the network performance of MANET.