1.- Install the McAfee Mobile Security app It's free.
2.- In the file explorer of your smartphone in options check the option> Show hidden files.
3.- And to make sure you download the VirusTotal app It's free.
The VirusTotal app only tells you what viruses or malicious apps are on your smartphone.
Then you go to: Settings> Applications> Clear cache> Clear data and Uninstall. And ready now we can restart the terminal and make a backup, and if you did not have an antivirus to install it to save you problems if it was the case that you like to install apps and video games outside the Google Play store.