Developers can connect an iOS device to their PC and install an app for testing. To achieve this, they must enable Developer mode.
If Developer mode is active on your device but you’ve never used it for development, it could mean that someone has accessed your device and installed an unwanted program.

To check for developer mode:
1. Launch the Settings application.
2. Tap Privacy and Security.
3. Under Security, tap Developer Mode.
4. If Developer Mode is enabled but you have never used your device for development, disable it and check your home screen (including folders) for any unrecognized apps.