A New Vulnerability in the Android Framework: Fragment Injection
We have recently disclosed a new vulnerability to the Android Security
Team. The vulnerability affected many apps,including Settings (the
one that is found on every Android device),Gmail,Google Now,DropBox
and Evernote. To be more accurate,any App which extended the
PreferenceActivity class using an exported activity was automatically
vulnerable. A patch has been provided in Android KitKat. If you
wondered why your code is now broken,it is due to the Android KitKat
patch which requires applications to override the new method,
PreferenceActivity.isValidFragment,which has been added to the
Android Framework.

http://securityintelligence.com/new-vulnerability-android-framework-fragment-injection/
http://securityintelligence.com/wp-content/uploads/2013/12/android-collapses-into-fragments.pdf