You downloaded a "modded" game or a free utility app from an unofficial source, and this file was hidden inside the package.
The app could track your keystrokes, steal your contacts, or access your photos.
Technically, an APK (Android Package Kit) is the file format used to install apps on Android. While legitimate apps like Facebook or Spotify use clear names, is a randomized string of characters.
Your phone may start showing full-screen ads even when you aren't using an app.
If you see this file on your device, Follow these steps instead:
Go to Settings > Apps and look for anything you don't recognize or that has a blank icon/name. Uninstall it.
What is OTTMTYvX.apk? Stay Safe from Suspicious Android Files