Oil giant Chevron was struck by the Stuxnet virus, a sophisticated cyber attack that tore through Iran's nuclear facilities and is believed to have been launched by the United States and Israel.
A Chevron spokesman told AFP Thursday that the virus had struck the oil giant in 2010 without causing any damage, confirming a report in the Wall Street Journal.
The virus was reportedly designed by US and Israeli intelligence to spy on and disrupt Iran's nuclear enrichment centrifuges, which Israel and the West believe is part of a secret nuclear weapons program, charges denied by Tehran.
Stuxnet—which was designed to attack computer systems designed by German industrial giant Siemens for managing water supplies, oil rigs, power plants and other critical infrastructure—has turned up in other countries.
Analysts and former US military officers have touted cyber attacks as a more effective weapon against Iran's nuclear ambitions than bombing raids, which they say would carry big risks without causing permanent damage to the program.
But Chevron officials said the virus spread beyond Washington's control.
"I don't think the US government even realized how far (the virus) had spread," Mark Koelmel, who oversees earth-science research and development at Chevron, told the Wall Street Journal.
"I think the downside of what they did is going to be far worse than what they actually accomplished," he added.
Neither the United States nor Israel has ever officially acknowledged the Stuxnet program.
Explore further: US, Israel made Flame virus to thwart Iran: report