Android activity back button

http://stackoverflow.com/questions/4779954/disable-back-button-in-android

Override the onBackPressed method and do nothing if you meant to handle the back button on the device.

@Override
public void onBackPressed() {
}

Requires API Level 5 or higher.

force stop:

http://stackoverflow.com/questions/5100728/how-to-force-stop-my-android-application-programatically