DHS ICS-CERT MONITOR report reveals that most critical infrastructure attacks involve APTs, but organizations lack monitoring capabilities. ICS/SCADA system were also targeted by other categories of threat actors, including cyber criminals, insider threats and hacktivists. Most common flaws exploited by attackers include authentication, buffer overflow, and denial-of-service. The majority of the attacks involved entities in the Energy sector followed by Critical Manufacturing, followed by the aviation and aerospace components. 38 percent of the reported incidents, the victims were not able to identify the attack vector exploited by hackers.”]
Source: https://securityaffairs.co/wordpress/34936/cyber-crime/ics-cert-monitor-report-apt.html