Hello. I downloaded a game from internet (not google play store) to my tablet (galaxy tab S) after playing a while, the tablet turned itself off without me doing anything and it said android is upgrading. then my phone started showing ads and installing apps without my permission. i deleted the game but it didnt help. there is a new app im not able to remove or disable.... it even wasnt device admin... i even tried factory reset, but it didnt do anything. The phone is fully stock and not rooted. im not going to reinstall my rom or root the phone. i dont have pc to do it with and i might risk breaking it. How did this happen and how can i fix it?