My wife has had a Samsung Galaxy J7, and one fine day we were visiting New York City, where, to make more photos, we went into a pretty solid looking phone store and bought what seemed like a genuine SanDisk SD card. It was not some cheap crap from a sidewalk sales scam. Once she inserted that card, it gave problems, never worked well, some fraudulent fake. But worse yet, it infected her phone with a viciously virulent virus which we could never again get removed. Brought it to several technicians already, but they were unable to fix it. Factory reset, of course, several times, and every time the virus is there. I am almost certain that these technicians tried to flash the firmware also, yet the virus crap keeps coming back. What could this be? I am flabbergasted. Is there really some corner of memory that is completely unreachable by factory reset and flashing the firmware? Could be that it somehow hooks itself into the thing that is used to lock the phone onto a specific provider, that too doesn't go away by flushing firmware. So, what is the approach to get rid of this virus, or is it that one must write off that phone as a total loss? IMO this is a reason not to buy mainstream brands of phones. I bet with my Xiaomi phone this could never have happened. Right?