Possible cyber intrusions targeting water and wastewater utilities have now been reported in at least a dozen states, multiple sources told ABC News.
There have been no widespread disruptions to water supplies or wastewater treatment so far, sources said.
The FBI is urging utilities to disconnect systems from the internet where possible, use systems with breakers and become familiar with reverting to manual controls if automated systems are compromised.
In Michigan -- one of the states affected -- state police said they are monitoring the situation and coordinating with federal partners.
The Michigan State Police said the FBI is leading the investigation and referred additional questions to the bureau.