Sorry for not answering earlier.
If I'm not mistaken, all passwords in the backup are file are encrypted just like in the app. While this won't hold of hackers with a major interest and enough time on their hands, it's about as secure as in the app itself. You should always make sure to keep the backups in a safe location.
That said, I'll consider adding an option to emit the passwords from the backup file but the ToDo list is very long. So no promises, sorry!