The networks powering industrial control systems have been breached more than 125 times in the past decade, with one resulting in U.S. deaths, a control systems expert said Thursday.

Joseph Weiss, managing partner of control systems security consultancy Applied Control Solutions, didn't detail the breach that caused deaths during his testimony before a U.S. Senate committee, but he said he's been able to find evidence of more than 125 control systems breaches involving systems in nuclear power plants, hydroelectric plants, water utilities, the oil industry and agribusiness.

"The impacts have ranged from trivial to significant environmental damage to significant equipment damage to deaths," he told the Senate Commerce, Science and Transportation Committee. "We've already had a cyber incident in the United States that has killed people."