Politicians in Vermont, including the Democrat Governor, Peter Shumlin, are calling for a full investigation into the incident.
"Vermonters and all Americans should be both alarmed and outraged that one of the world's leading thugs, [Russian President] Vladimir Putin, has been attempting to hack our electric grid, which we rely upon to support our quality-of-life, economy, health, and safety," he said in a statement.
Democratic congressman Peter Welch said the discovery showed "how rampant Russian hacking is".
"It's systemic, relentless, predatory," he added.