Cloud computing is one of the most emerging networking technology, which has been considered as significantly effective among different types of users. Using cloud computing can be cost effective and organisation can focus more on their unique business idea instead of IT infrastructure or developing software, if they use IaaS or SaaS according to the business needs. However, there are issues with security of critical business data that is stored on cloud service provider's server. There are many concerns in regards to cloud computing security, which have many vulnerabilities and threats. In our previous paper, we have investigated security issues for cloud computing environment, where we have revealed the lack of awareness of cloud service providers to ensure the security. In this paper we have discussed about more threats and vulnerabilities of cloud computing, which cover some of the technical aspects of this burning issue. We would like to propose a cost effective and efficient security model for cloud computing environment after identifying the security risks involved in this sector of modern computing.