It probably was the phone OS shipping with malware, but there is a different route that effects all phones, including iOS. It's happens the authors loose inter

It probably was the phone OS shipping with malware, but there is a different route that effects all phones, including iOS. It's happens the authors loose interest in maintaining their apps. Malware authors then purchase their developer keys, issue an update (but change nothing else), and you find yourself being woken up at 2AM in the morning by some screeching Casino ad. Or at least that's what my wifes phone did to her, and of course it was immediately my problem. I don't know if Android has an Update History for apps now, but back then it didn't. You don't know what app it is, because all the normal functional is untouched so it works as before. In my case there were two of them - which was worse because my technique was to uninstall one by one, then re-install if the problem continued. After a week or two of experimenting I found the right combination of apps to uninstall and my nights became peaceful again. The Play store cleaned them out after a while of course, but it was painful at the time.