The Natanz computer systems were “air gapped” from the outside, meaning they had no connections to the Internet. The CIA and the Israelis endeavored to slip the code in on USB keys, among other techniques, with the help of both unwitting and witting Iranian engineers. With some hitches, the plan worked reasonably well for several years. The Iranians were mystified about why some of their centrifuges were speeding up or slowing down and ultimately destroying themselves.
