Cyber warfare used to be the stuff of sci-fi movies and military exercises. But with the advent of the Stuxnet worm, the Sony Pictures hacking—which was allegedly carried out with the backing of the North Korean government—and this week’s assault on German government websites, large-scale cyber attacks with suspected ties to nation states are growing increasingly prevalent.

Few people have lifted the veil on cyber warfare like Edward Snowden, a former NSA contractor who leaked a massive number of documents to the press.