Dependable and secure computing has grabbed the spotlight and has pioneered the fusion between dependability and security since 2000. The field of dependability has progressed to be an internationally active field of research. The objective is to explicate a set of attributes that includ es reliability, security, safety, availability, confidentiality, integrity and maintainability. Due to the increasing reliance on computer systems in most societies, the field is of growing importance. It has

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... ntrol over the physical access to the hardware and also provides protection against harm that may come via network access and code injection. Malpractice done by operators, whether intentional, accidental, or due to them being tricked can also be controlled. Also the rapid increase in mobile applications, computers, and wireless networks has modified the characteristics of network security. A series of Internet attack and fraudulent acts on individual network and companies have shown that open computer networks have no immunity from intrusions. The purpose of the paper is to provide review of the existing literature available in the dependable and secure computing domain. The paper also presents an overview and study of the network security metrics with several security threats, security issues, security solutions and currently used methodologies to overcome it.