The newest of them, ProtonMail, attracted widespread attention after the main character on the hit hacking show Mr. Robot used it. But just how secure is it?

Email applications that say they're strong enough to foil government snoops and advertisers too often have chinks in their armor. Four years ago, a federal judge forced the now-defunct secure email company Lavabit to turn over its encryption keys to the government, having earlier claimed its service was "so secure that even our administrators can't read your email." Going further back, we learned that encrypted email provider Hushmail was totally cool with spilling secrets to the government, which it did by grabbing user passwords to decrypt email and turning them over to law enforcement in plaintext. It, too, claimed that even its own admins couldn't read the encrypted email.

But ProtonMail, founded in August, 2013, by scientists who met while working at the European Organization for Nuclear Research in Geneva, seems to offer protections other email services don't.