Facebook will now notify users via email and the Facebook App when their account is used to login into a third-party app or website (Mariella Moon/Engadget)

Mariella Moon / Engadget:
Facebook will now notify users via email and the Facebook App when their account is used to login into a third-party app or website  —  It´s pretty easy to forget where you use your Facebook credentials to log in, especially since using it is as easy as clicking a single button.