'Unkillable' Android malware



In too deep
When the malware is first installed, it downloads a 'dropper' trojan, which collects information on your device and installs another trojan. This then downloads exploit code that gives it root access to your device, where it can cause whatever mayhem its creators see fit.

Removing the infection is extremely difficult. All these downloads are hidden deep in the system files, making them hard to find, and the dropper that's installed in the system partition can start the process all over again even after a factory reset.

Golovin advises reflashing the phone, but warns that sometimes the factory-installed firmware might contain xHelper, in which case there's very little you can do. "If you do use a different firmware, remember that some of the device’s components might not operate properly," he advises.

see the link for details