Around 40% of gratis Androids apps report on the user's actions to Facebook.

Often they send the machine's "advertising ID", so that Facebook can correlate the data it obtains from the same machine via various apps. Some of them send Facebook detailed information about the user's activities in the app; others only say that the user is using that app, but that alone is often quite informative.

This spying occurs regardless of whether the user has a Facebook account.