No cyber or physical attacks against the power grid were successful last year, but that doesn’t mean the country’s electric supply is safe, according to the nation’s electric reliability watchdog.

“While there were no reportable cyber security incidents during 2016 and therefore none that caused a loss of load [or power], this does not necessarily suggest that the risk of a cyber security incident is low,” said the North American Electric Reliability Corporation in its 2017 State of Reliability report released Thursday.