Any application that has not been downloaded from Google Play, those who post the application in the public domain made any changes to it, and this is not necessarily a virus, although it does. It gives an opportunity to bypass payment, which ultimately affected the phone in a foreseeable way. If you installed the application through the App Installer - most likely this application was not official, for watching movies for example. I also think that if you reset to factory settings everything will return to normal. And if not, you should go to a service center.