How do I stop Android to auto enabling allow unknown sources?
This also happened to my phone. Even after several flashes, the torrent of annoying self-install apps keeps happening. Malwarebytes I used can't touch the last infected file; the system settings itself. Even right after flashing the third time, apparently the settings app which is the backbone of everything has been compromised from the get go.
My findings suggest that this was a known vulnerability issues and Google acknowledge it. Alas, there are still no solution nor updates to rectify it other than suggest user to stop using the phones that use 5.1 altogether. FML.
So, out of rage, I took drastic measure. I delete the settings app with the help of Root Explorer. Of course, I've made certain preps before I did, since I'm fully aware the consequence once I did.
Now, I can't even connect my phone to my PC via USB, nor I am able to log in a new Wi-Fi spot. A price I pay just to save my data cap from being drained by involuntary app download.