Facebook scans the contents of messages that people send each other on its Messenger app, blocking any content that contravenes its rules, it has emerged.
The scandal-hit firm, still reeling from the Cambridge Analytica debacle, checks images and links for illegal or extreme content using automated systems.
What you write in your messages may also be read manually if it's flagged to moderators for breaching Facebook's community guidelines.
While the intentions behind the practice may be well-meaning, the news is likely to add to users' concerns over what the social network knows about them.
It follows revelations that the Trump-affiliated consulting firm obtained data on at least 50 million unsuspecting Facebook users.
This information was used to target voters in the US, based on psychological profiling, with political adverts spreading disinformation.
Facebook is also facing criticism for collecting years of data on call and text histories from Android users