The most critical and worst target of a State-sponsored cyber-attack s could be Hospitals, Dams, Dykes and Nuclear power stations. Monju Nuclear Plant in Tsuruga, Japan was accidentally targeted by a malware on 2nd January, when a worker updated the system to the latest version of the video playback program. The malware itself is not much sophisticated like Stuxnet or Duqu, but the unmanaged software update and patch management system can seriously lead to a critical cyber attack.
Source: https://thehackernews.com/2014/01/rogue-software-update-cause-malware_9.html