Stuxnet was a virus, probably written by the government of the USA or Israel.
Unlike most viruses, it was targeted at one particular computer. Someone to insert a USB (Universal Serial Bus) containing the virus into one of Iran’s highly secure computers.
This could have been done by losing some infected USBs (Universal Serial Bus) near the facitily and trust some boob might insert it into a secure computer
to find out what was on it, perhaps some porn.
It exploited three unpublished OS (Operating System) vulnerabilities of the OS. It moved from machine to machine until it found
the target computer that controlled the centrifuges used to enrich uranium. It then sent commands to damage the centrifuges by running them
too fast, and to ruin long enrichment runs my varying the speed. It did not actually infect the hardware controllers as some reports
stated. To pull this off, the perpetrator needed some very detailed knowledge of how the computer controls worked. The perpetrator would then also
know precisely how much enrichment was being done — for electric power or for weapons. Given that the Iranians have offered inspection,
it seems most likely the degree was for power. The perpetrator did a pre-emptive strike, destroying electric power.