Google has been cracking down on potentially harmful apps being installed from the Play Store, so much so that currently, as of Google's latest security report, only 0.15% of Android devices have been able to successfully install PHAs or potentially harmful apps. Google first started the initiative in which several OEMs became participants in. Stagefright was the first real security problem that faced Android since the beginning of the Android Platform. The vulnerability took advantage of a bug present in the method used to preview multi-media messages received through an SMS...
Source: http://www.gsmarena.com/google_releases_annual_security_report_harmful_app_installs_have_drastically_dropped-news-17841.php
