WASHINGTON — IN Moscow this summer, while reporting a story for Wired magazine, I had the rare opportunity to hang out for three days with Edward J. Snowden. It gave me a chance to get a deeper understanding of who he is and why, as a National Security Agency contractor, he took the momentous step of leaking hundreds of thousands of classified documents.

Among his most shocking discoveries, he told me, was the fact that the N.S.A. was routinely passing along the private communications of Americans to a large and very secretive Israeli military organization known as Unit 8200. This transfer of intercepts, he said, included the contents of the communications as well as metadata such as who was calling whom.

Typically, when such sensitive information is transferred to another country, it would first be “minimized,” meaning that names and other personally identifiable information would be removed. But when sharing with Israel, the N.S.A. evidently did not ensure that the data was modified in this way.

Mr. Snowden stressed that the transfer of intercepts to Israel contained the communications — email as well as phone calls — of countless Arab- and Palestinian-Americans whose relatives in Israel and the Palestinian territories could become targets based on the communications. “I think that’s amazing,” he told me. “It’s one of the biggest abuses we’ve seen.”