David Nicklin brings a story that has a moral: friends don’t let friends install apps on their iOS devices:
I was traveling overseas a couple of years ago for a friend’s wedding. While there, I spent an afternoon with a long-lost acquaintance. Somehow, for whatever reason, he shared an iOS app with me, installing it on my phone and using his Apple ID. Up until I bought a new phone and restored it from backup, everything was fine. Now, however, the phone is asking me for his Apple ID credentials.
I don’t even remember which app it was he installed for me. Is there any way to easily find which app is causing the problem without uninstalling every app on the phone and re-installing them until I find what I am looking for?
Read more here:: Find out which iOS app is requesting your Apple ID password