Smart grid uses the power of information technology to intelligently deliver
energy to customers by using a two-way communication, and wisely meet the
environmental requirements by facilitating the integration of green
technologies. Although smart grid addresses several problems of the traditional
grid, it faces a number of security challenges. Because communication has been
incorporated into the electrical power with its inherent weaknesses, it has
exposed the system to numerous risks. Several research papers have discussed
these problems. However, most of them classified attacks based on
confidentiality, integrity, and availability, and they excluded attacks which
compromise other security criteria such as accountability. In addition, the
existed security countermeasures focus on countering some specific attacks or
protecting some specific components, but there is no global approach which
combines these solutions to secure the entire system. The purpose of this paper
is to provide a comprehensive overview of the relevant published works. First,
we review the security requirements. Then, we investigate in depth a number of
important cyber-attacks in smart grid to diagnose the potential vulnerabilities
along with their impact. In addition, we proposed a cyber security strategy as
a solution to address breaches, counter attacks, and deploy appropriate
countermeasures. Finally, we provide some future research directions