Smart grids are considered as one of the most revolutionary technologies in the field of power and communication. However, security management of such a big infrastructure is a key challenge for the research community of the world. In this context, this paper provides the major security goals of smart grid systems along with classification of different vulnerabilities. Additionally, we also present remedial measures to prevent these security threats. In the end, we provide conclusions and future works to finalize the analysis of security issues in smart grid.