What is the most sophisticated piece of software/code ever written?

Stuxnet was one great piece of malware.

Quora.com:

You would never expect that all those problems were caused by a computer worm, the most devious and intelligent computer worm in history, written by some incredibly secret team with unlimited money and unlimited resources, designed with exactly one purpose in mind: to sneak past every known digital defense, and to destroy your country’s nuclear bomb program, all without getting caught.

Stuxnet was one great piece of malware.