Here's something you probably didn't know: Facebook has a team of employees who read your private messages if they have been flagged by an automated tool. The tool searches for content that appears to violate their terms of service, namely malicious (infected) URLs or child pornography. It's imperfect, of course — that's where humans come in.

If a private message is flagged, actual people will jump in and read it. If there is something that could be illegal — particularly regarding child exploitation — those people contact law enforcement. The intent here is clear and defensible, yet the fact remains: All that stands between your "private" messages and the eyes of a stranger is the snap judgment of an algorithm.

"There are strong internal controls around the use of these tools to prevent misuse and abuse," Facebook told BuzzFeed, "and stringent guidelines for the way we cooperate with law enforcement."

It's not just Facebook. Dating site OkCupid has humans read private messages that have been flagged by its users, as reported by San Francisco Public Press.

Even more troublesome, OkCupid's readers are sometimes regular users, not employees. These users are deputized to help hand the large volume of "flagged" messages and can view ongoing conversations that may contain private information, whether or not the flagging users' claims are legitimate.