Peter Maass in the NYT:

Before long, Poitras received an encrypted message that outlined a number of secret surveillance programs run by the government. She had heard of one of them but not the others. After describing each program, the stranger wrote some version of the phrase, “This I can prove.”

Seconds after she decrypted and read the e-mail, Poitras disconnected from the Internet and removed the message from her computer. “I thought, O.K., if this is true, my life just changed,” she told me last month. “It was staggering, what he claimed to know and be able to provide. I just knew that I had to change everything.”