The concept of cloud computing can be traced back to almost the middle of last century. Cloud paradigm offers scalable, portable, platform-independent, ubiquitous, shared resilient, sustainable, and near-utility computing. The cloud computing is implemented as a software-only solution or based on advanced hardware supported virtualization technology. This paper presents the fundamental technology behind the cloud computing. Cloud computing posit as a utopia to solve multitudes of challenges of the current time. But in practice security is a major road block to its widespread adoption. This paper discusses the security issues of the cloud computing. Further the paper illustrates upon the security solutions for the virtualization and web services, two major enabling technologies of cloud computing. It also explains the novel concept of integrating the multi-level security in all of the cloud offerings in contrast to the security-as-a-service concept. Finally paper mentions the important guidelines for the development of service level agreements.
The cloud computing paradigm has characteristics envisioned since almost the middle of last century. It offers scalable or elastic computing on virtually complete range of computing devices, supporting all existing and archaic software technologies and tools, and served through disparate network hence making it platform independent, portable and ubiquitous. Similarly capability to serve on-demand, share and instant commissioning and de-commissioning of configurable computing resources causes it to be resilient, sustainable and near-utility computing. It offers services in three major categories Software-as-a-Service (SaaS), Platform-as-a-Service (PaaS) and Infrastructure-as-a-Service (IaaS) . SaaS refers to application software services, PaaS refers to application infrastructure services and IaaS refers to system infrastructure services. It is deployed under four schemes Private, Community, Public or Hybrid Cloud .
The cloud computing as institutionalized seems to bring the computing to common man’s life such as every individual having a virtual desktop on the cloud. And as the resource hungry world is facing tough time to commit its resources on burgeoning needs of computing such as the concept of smart cities and its operations  and evolution of Big Data to mention some . And sustainability of information technology is being questioned all the more . Cloud computing looks a silver bullet to meet range of challenges of the present world. Probably the only road block or hindrance to this panacea currently seems security threats or difficulty in achieving fully verified code.
The public cloud services market was at $175 billion in 2015 and is expected to grow at 16.5 percent in 2016 . This shows the general acceptability towards the adoption of the public cloud. The benefits of cloud computing are multidimensional such as economic, operational, business and technological. Adoption motivations range from factors such as financial gains due to pay per use mechanism, no long time commitment to the service providers, performance and management ease of Information Communication Technology ICT resources, scalability due to datacenter integration, higher utilization of resources due to multi-tenant (sharing) environment and virtualization .
On the other hand several barriers to adoption of cloud are also present in the literature. The study  has presented the barriers after surveying 95 Spanish industrial Small and Medium Enterprises (SME). The first and foremost barrier happens to be the security with respect to the whole paradigm itself such as network attacks. The security concerns such as confidentiality, integrity and availability are of paramount importance to the cloud computing adopters. Data today holds the same position as material resources and is needed in all the digitized processed of the organizations without compromising the accuracy, privacy and ownership. Data is also required to fulfill the confidentiality and law requirements of individual nations. And in the multi-party and cross border ICT infrastructure data compliance assurance is a strong deterrent for the potential cloud adopters. Likewise the absence of strong business case having cost benefit analysis and difficulty in switching the service providers have been mentioned as barriers .
Therefore, where there are apparent benefits of public clouds, there also exists real concerns regarding the security, privacy and control of the data; availability, scalability, performance and cost-effectiveness of public cloud infrastructure; and due diligence of the public cloud service provider. This study aims at following objectives:
• The underlying technology of cloud computing and its institutionalization.
• The existing security threats in cloud computing.
• The security solutions adopted by the cloud computing community.
This paper is organized into five sections. First present section, Introduction, gives the basic concept of the cloud, its benefits and barriers to its adoption and the objectives of this study. Second section, Cloud Computing Technology, presents the important technological components that make cloud computing work and its implementation model. Third section, Cloud Computing security threats, delves into literature to identify the numerous security risks in the public cloud environment and present the security threat classification framework. Fourth section, Cloud Security Solution discusses important guidelines and frameworks to secure the virtualization and web services. This section also presents the novel concept of multi-level integrated cloud security concepts and important guidelines to design the document of service level agreements. Finally the fifth section concludes the study.
II. CLOUD COMPUTING TECHNOLOGY
The evolution of cloud computing can be traced back to the concept of virtualization and non-interference proposed in 1980s  or even to the later period of 1950s to the concept of virtual memory . Virtualization in cloud computing context refers to hosting a unified and uniform view of disparate hardware resources to guest system and application software. The cloud computing rests on an important component called as Hypervisor that facilitates the hardware sharing through a masquerade known as virtualization. Generally speaking there are two types of hypervisors, also called as the virtual machine monitors (VMM). The type-1 or bare –mental hypervisor runs on top of hardware and manages different guest operating systems or virtual machines (VM). Whereas type-2 or hosted hypervisor runs on top of operating system and manages different VMs as processes. There are several hypervisor in the market such as Xen, VMware ESX and ESXi, Microsoft Hyper-V, Citix XenServer, Redhat KVM, Oracle VM Server etc.