Modern critical infrastructures (e.g., power plants, energy grids, oil pipelines, etc.), make nowadays extensive use of information and communication technologies (ICT). As a direct consequence their exposure to cyber-attacks is becoming a matter of public security. In this paper, we analyse a particular infrastructure, rarely considered as source of threats, on which indeed the majority of network based services rely: the domain name system. Taking as example the power system, we show how deeply a failure (accidental or malicious) of the DNS might impact on the operation of the modern and distributed critical infrastructure.