The Cybersecurity and Infrastructure Security Agency (CISA) and the National Security Agency (NSA) have issued a joint advisory warning that foreign hackers are targeting systems that support US critical infrastructure.
The advisory urges critical infrastructure operators to secure their operational technology and control systems as soon as possible.
The advisory lists several “recently observed tactics, techniques, and procedures,” including spear phishing, ransomware, connecting to Internet-accessible PLCs that do not require authorization for initial access, and modifying control logic and parameters on PLCs.
Here is a link to Defense.gov with the full warning text: (PDF)
https://media.defense.gov/2020/Jul/23/2002462846/-1/-1/1/OT_ADVISORY-DUAL-OFFICIAL-20200722.PDF