Advanced Metering Infrastructure (AMI) is envisioned to have the potential to revolutionize the power grid making it the 'Smart Grid'. AMI, through the use of 'smart meters' and high-speed networks, promises to strengthen both the stability and sustainability of the grid. The vision of AMI is to enhance and improve the grid by providing fine grained control over pricing and usage to both the utility and the customers. The promise is so convincing that there have been rapid large scale deployments all over the world in a very short time. In this frenzy of excitement, security of AMI, an issue of utmost importance may have been overlooked. In this paper, we present preliminary work of an in-depth study of vulnerabilities in AMI against cyber attacks. We point out vulnerabilities in ANSI C12.22, the protocol specification for interfacing smart meters with data networks. We also show how these vulnerabilities can be used to launch denial of service (DoS) attacks on the AMI and then propose potential solutions.