Bluebox Security has released an App to check if your Android device is still vulnerable to the “master key” exploit. There is a patch out from Google, but not all handset providers have implemented it in their distros yet…
Check out this article if you want to know more about this expoit.
http://bluebox.com/corporate-blog/bluebox-uncovers-android-master-key/
And this article about it being patched by Google.
http://www.engadget.com/2013/07/09/google-plugs-android-security-hole/