It's not just bad guys who want to hide the content of their e-mails. So, too, do inventors, attorneys, investors, scriptwriters and others who may want to encrypt their correspondence so it can't be read by rival parties in business deals. But just the act of encryption can also be suspicious, Blake said.
Some encryption measures may work, other can be broken by NSA mathematicians. Also use of Tor, a software program designed to help foreign activists evade government censorship in places like Egypt, Syria or Libya, may also be triggering NSA searches domestically. "There's a paradox of privacy," he said. "Even a lot of the standard layers of protection, the email providers only provide (encryption) when the e-mail is transmitted, not when it is stored, which still makes you vulnerable."
An U.S. based encrypted e-mail service, Lavabit, shut itself down last week, rather than comply with government orders.