Blog post and analysis by Vojtech Bocek and Nikolaos Chrysaidos
When you get a brand new phone, you expect it to be clean from any malware and adware. Unfortunately, this is not always the case. The Avast Threat Labs has found adware pre-installed on several hundred different Android device models and versions, including devices from manufacturers like ZTE, Archos, and myPhone. The majority of these devices are not certified by Google.
Article Link: https://blog.avast.com/android-devices-ship-with-pre-installed-malware