File Substitution Hack is when by changing the content of the file, but not the file name, attacker can modify behavior of a program.
It is very common in virtual currency on iOS, that is how players have “unlimited” virtual currency in games.
On application that is on Apple App Store, File Substitution Hack result in decline of sale of virtual currency (In-App Purchase), basically you as app developer lose money.
You will receive iOS framework, just with drag-and-drop it is integrated in your project.
It is tested from IOS 6.0, so it is working on any iOS device.