: Unverified APK files can secretly log your keystrokes, steal your passwords, or access your private photos and messages.
Because "MFF" can stand for many different things and "0.5" looks like an incredibly early beta version number, downloading a file with this exact name from third-party sites carries high security risks.
Depending on what you are looking for, you may be referring to one of these legitimate applications:
: This is the most popular global app carrying these initials. It is a highly successful action-RPG mobile game developed by Netmarble where you build teams of Marvel superheroes and villains.