https://arstechnica.com/information-technology/2019/04/mysterious-safety-tampering-malware-infects-a-2nd-critical-infrastructure-site/

Sixteen months ago, researchers reported an unsettling escalation in hacks targeting power plants, gas refineries, and other types of critical infrastructure. Attackers who may have been working on behalf of a nation caused an operational outage at a critical-infrastructure site after deliberately targeting a system that prevented health- and life-threatening accidents.