For more than 30 years, the United States took widely publicized, drastic measures to hinder nuclear development in Iran. But amid sanctions and diplomatic efforts and under pressure from Israel, the U.S. government secretly launched an unprecedented weapon at Iran’s nuclear facilities.

“The Iranian nuclear program was a national issue for the Iranian people, and once the industrial sabotage happened, Iran developed a very proactive presence in cyber domain,” says Emad Kiyaei, executive director of the American Iranian Council. He is talking about Stuxnet, a self-replicating computer virus that disrupted 20 percent of Iran’s nuclear centrifuges. Discovered in 2010, it was the first highly public instance of state-supported cyberwarfare and is one of the subjects of filmmaker Alex Gibney’s new documentary, Zero Days.