Bitcoin wallets on Android are vulnerable to theft because of problems in a component that generates secure random numbers and the statement is said and supported by many developers around the globe.There is a huge problem that is such that the Bitcoin wallets generated by an Android app is affecting the Android OS.
Mike Hearn ( Software Developer at Bitcoin Developer Forum ) reported ;
As a result all private keys generated on Android phones/tablets are weak and some signatures have been observed to have colliding R values, allowing the private key to be solved and money to be stolen. If you use an Android wallet then we strongly recommend you to upgrade to the latest version available in the Play Store as soon as one becomes available and once your wallet is rotated, you will need to contact anyone who has stored addresses generated by your phone and give them a new one.
There is a lot more which is said about the same and you could view other sources to seek more information.