i have done research on securing android application, finding are listed below:
I tried installing few application from the Android market using the pre-installed Market App. From that I learned that an unauthorized persons can not use extract or install android applications, which is in the android market. As Android market won't provide the apk files, it just installs the applications, but the user can still install the application n number of times, even though if he had deleted that application.
Here are some text extract from Android Developer site
To Launch the Market Application on a Device:
Android-powered devices include a pre installed Market application that gives users access to the Android Market site. From Market, users can browse or search available applications, read ratings and reviews, and download/install applications.
Publishing Updates on Android Market:
At any time after publishing an application on Android Market, you can upload and publish an update to the same application package. When you publish an update to an application, users who have already installed the application will automatically receive a notification that an update is available for the application. They can then choose to update the application to the latest version.
So finally we need not bother about the Securing of our application from the un authorised persons
Thanks and Best Regards