Zuckerberg removed a line about monitoring private messages from his manifesto
If Gmail reads private emails to target ads [1], why would people think that Facebook isn't doing the same thing? Also many companies (including Facebook) have agreed to share hashes and cooperate to "remove extremist content from their websites" [2]. It would be naive to think that they are excluding private messages from their searches.[1] https://www.theguardian.com/technology/2014/apr/15/gmail-sca...
[2] http://www.reuters.com/article/us-internet-extremism-databas...