I think the primary suspect today is app analytics platforms, especially the free ones like Facebook's and Google's. Just looking at how e.g. Intercom pulls add

I think the primary suspect today is app analytics platforms, especially the free ones like Facebook's and Google's. Just looking at how e.g. Intercom pulls additional data about users that your app didn't provide (full name, photo, Twitter or LinkedIn profiles etc), you realize that these 3rd party app services know more about you than you'd like them to. In fact Intercom, unlike others, inadvertently exposes this spooky fact that they are a part of the giant spying octopus with N number of independent brains. So the explanation of what happened with the pregnancy app in the article might lie in 3rd party frameworks linked to the app. It might be that the app uses Facebook for its analytics but it's not even necessary: it could be Mixpanel, Amplitude, Segment, Fabric, Intercom, any or all of them. The spooky part here is that the legal implications of what 3rd party app services can do with data are not very clear (to me at least), and on top of that, tracing the sources of information seems to be getting more and more difficult these days. Facebook's answers to the author might be kind of honest: the people you talk to may not know where the information is coming from. N.B. use outline.com if you can't see the linked article.