In recent days cloud computing and cloud-based service, provisions play a vital and significant role in Internet-based information computing. It interrelates various applications like sales, purchase, banking, customer service, etc. and it behaves entirely as a service-oriented platform or environment. The primary objective of the cloud computing is sharing the resources within increased efficiency regarding time and cost for all kind of customers who needs a cloud service badly and immediately. Though the energy is high, it cannot assure that the cloud computing, service providing, and customer maintenance are highly secured. Service providers in the cloud are not strictly public; it may be private, community and hybrid. Malicious activities can be created or occurred in the middle of the communication and it is difficult to predict a particular person in the middle becomes a malicious user, from where and how. Secured data transmission and discussion in cloud computing considered as the main problem, and various earlier research works focused on tightening the security. The primary objective of this paper is to discuss different security mechanisms applied to multiple malicious threats in the cloud to understand the various issues and challenges faced in earlier research works. It provides a summary of the risks, appropriate method and the limitations and it helps to understand the primary and main problems related to security.