Android 6.0 / Facebook/ 3rd party apps
What I found interesting was that some Android devices that came with the Facebook app already installed had two other Facebook related apps pushed on to the devices after updating to Android Marshmallow.
If I understand correctly the newly installed Facebook apps (Facebook Installer, Facebook Manager) allowed Facebook to update and/or modify the Facebook app independently without needing the Google Play Store.
Even with the Facebook app uninstalled the two other apps remained and still used data in the background.
I have also seen apps on third party app stores that are known to host questionable repackaged, modified and resigned apps that also contained Facebook's Graph API.