the target was seemingly impenetrable

The target was seemingly impenetrable; for security reasons, it lay several stories underground and was not connected to the World Wide Web. And that meant Stuxnet had to act as sort of a computer cruise missile: As it made its passage through a set of unconnected computers, it had to grow and adapt to security measures and other changes until it reached one that could bring it into the nuclear facility.

When it ultimately found its target, it would have to secretly manipulate it until it was so compromised it ceased normal functions.

And finally, after the job was done, the worm would have to destroy itself without leaving a trace.

That is what we are learning happened at… (continue)