The Facebook news feed is public and Messenger is private…right? Not quite: Facebook routinely scans your Messenger conversations, and in some cases human employees may review them.

The new first broke in a Mark Zuckerberg interview by Ezra Klein, when Zuckerberg offhandedly mentioned the company was reviewing manipulative Messenger posts spreading through Myanmar. Sarah Frier, writing for Bloomberg, followed up on this, and found that some scanning and filtering happens constantly:

The company told Bloomberg that while Messenger conversations are private, Facebook scans them and uses the same tools to prevent abuse there that it does on the social network more generally. All content must abide by the same “community standards.” People can report posts or messages for violating those standards, which would prompt a review by the company’s “community operations” team. Automated tools can also do the work.

Facebook, for what its worth, says that Messenger conversations are not scanned for advertising purposes. I can’t help but wonder how long that stays true—Google’s Gmail has scanned personal messages to serve targeted ads for over a decade.