The Maine Department of Environmental Protection (DEP) urged water treatment facilities across the state to take security measures after Iran was accused of a cyberattack that impacted water systems across multiple states.

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Most estimates suggest that seven states were impacted last week—with Minnesota suffering attacks against 30 individual facilities—while Axios reported that the attacks targeted at least 12 states.

Multiple outlets reported that U.S. officials and cybersecurity experts attributed the cyberattacks to Iran, though President Donald Trump expressed a belief that Iran was not responsible for the failures in water systems.

Regardless of which hostile power launched the attack, the Maine DEP is urging water infrastructure facilities to implement security measures.

Measures include strong passwords, changing credentials, separating information technology from operational technology, and removing vital industrial programmable logic controllers (PLCs) from direct contact with the outside internet.

The DEP also urged facilities to report any suspicious activities and incidents to law enforcement, tech providers, and DEP inspectors.

The recent cyberattack exposes a significant weakness in U.S. infrastructure that can be exploited by foreign adversaries such as Iran or China to potentially shut down drinking water or other essentials in the U.S. without firing a shot.