Woo. Woo. Alex Hern reporting for The Guardian:

In at least one previous version of the Messenger app, Facebook only told users that the setting would enable them to “send and receive SMS in Messenger”, and presented the option to users without an obvious way to opt out: the prompt offered a big blue button reading “OK”, and a much smaller grey link to “settings”.

Nowhere in the opt-in dialogue was it made clear that text histories would be uploaded to Facebook’s servers and stored indefinitely.