Abstract: The Android mobile platform has developed from its first phone in October 2008 to being the most popular smart phone operating system in the world by 2012. The explosive growth of the platform has been a significant win for consumers with respect to competition and features. The market has been booming in the past few years that, there are now over 1 million applications on the Android market. Due to the wide usage, it is necessary to provide users with security applications to manage the data in their personal smart phones. The Android platform has become one of the most popular operating system with millions of new users each year. If you don’t like the firmware the device manufacturer has installed on your Android device, you are free to replace it with your own custom firmware. Custom firmware is also the only way you can install newer versions of Android on devices that are no longer supported by their manufacturers.KEYWORDS— Dalvik - VM, OHA, AOSP , System Design ,firmware, Android.