In cloud computing, there are several security concerns. The security concern may increase due to one of the important techniques of virtualization. Cloud computing is also having several important characteristics which are used for its improvement and to provide several services to its end user. Some of the essential and important characteristics are on-demand self-service, broad network access, rapid elasticity, resource pooling, and measured services. By using these characteristics, cloud computing satisfies the needs of its end users, but the base to these characteristics is the virtualization technique. These observations depict the reason for several attacks and especially DoS and DDoS attacks or brute-force attacks. This article provides detailed information on these characteristics and also provides information about flaws and breaches. The reason is virtualization, which makes cloud computing insecure to use. Several techniques and algorithms are used to improve the cloud computing system, but flaws in their application have been discovered. These algorithms may degrade the quality of cloud computing system and may also makes cloud computing insecure to its end users. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.