Hundreds of U.S. utilities were penetrated by Russian hackers who could have disrupted the nation's power grid.

The attacks were launched last year by threat actors belonging to a group known as "Dragonfly" or "Energetic Bear," which is sponsored by the Russian government, The Wall Street Journal reported Monday.

The hackers used Black Hat tools such as phishing and waterhole traps to obtain credentials from legitimate users and leverage them to gain access to the utilities, the Journal noted, citing federal government officials. Read more.