They are fake and potentially harmful.
Section 5 — Performance Optimization
If you see a file named ModernWarfare2.apk that claims to be the full 2009 game, it is 99.9% fraudulent. Do not install it. Call Of Duty Modern Warfare 2 Apk Android
Section 1 — What This APK Is
Your friend is almost certainly mistaken. They may have: They are fake and potentially harmful
He spent the next three hours: