[TheGuardian] Email surveillance could reveal journalists' sources, expert claims

Phil Zimmermann, the creator of the email encryption software PGP, has warned that anyone who uses consumer email services needs to be aware of the threats of exposing their metadata to eavesdroppers. [...]

The US government insisted that that data was not private, but in aggregate it can build a detailed picture of people’s lives.

Zimmermann argues that unprotected metadata isn’t just dangerous in aggregate. “You're a journalist for the Guardian," he told this reporter. "You know that the Guardian sometimes writes stories that are of great interest to intelligence agencies. Well, what if the intelligence agencies want to see if a journalist at the Guardian is talking to a particular sensitive source?

You don't have to do a lot of data mining for that. All you have to do is find that so-and-so, some government employee, is talking to some journalist at the Guardian. Then somebody's in a heap of trouble.” [...]