d supports a specific community. The health-care industry is an example of an industry that is employing the community cloud concept. 2 Virtualization and Cloud Computing Private clouds offer the highest level of security and control. On the other hand, they require the organization to purchase and main- tain its own infrastructure and software, which reduces the cost efficiency. Besides, they require a high level of engagement from both management and IT departments to virtualize the business environment. Such a cloud is suited to businesses that have highly critical applications, must comply with strict regulations, or must conform to strict security and data privacy issues. A hybrid cloud comprises both private and public cloud services. Hence, it is suited to companies that want the ability to move between them to get the best of both worlds. For example, an organization may run applications primarily on a private cloud but rely on a public cloud to accommodate spikes in usage. Likewise, an organization can maximize efficiency by employing public cloud services for nonsensitive operations while relying on a private cloud only when it is necessary. Meanwhile, they need to ensure that all platforms are seamlessly integrated. Hybrid clouds are particularly well suited for E-commerce since their sites must respond to fluctuating traffic on a daily and seasonal basis. On the downside, the organization has to keep track of multiple different security platforms and ensure that they can communicate with each other. Regardless of its draw- backs, the hybrid cloud appears to be the best option for many organizations. In Table 2.1, we enlist the main benefits and risks associated with each type of clouds. Understandably, security is one of the main issues in cloud computing. There are many obstacles as well as opportuni- ties for cloud computing. Availability and security are among the main concerns [19, 20]. 2.1.3 Challenges Being a disruptive technology, cloud computing has gained significant momentum in the past deca