This is the part of the Stuxnet story that always fascinated me:

Also remember that this thing, in order to work, it needed to get into the kernel in order to set up a rootkit to protect itself. It needed to have digitally signed drivers. And we know where they came from, remember? They came from Realtek and JMicron, two companies in the same industrial park, same physical location. So it is believed that some agent broke into and physically compromised those facilities to steal their private keys for their credentials.

–Security Now! #291

https://en.wikipedia.org/wiki/Hsinchu_Science_Park