What is that copy protection stuff on the Adroid Market

Last time I released the previous version of jjReader on the Market dashboard, I check following option by mistake and unfortunately it is not undoable.

Copy Protection

Off (Application can be copied from the device)

On (Helps prevent copying of this application from the device. Increases the amount of memory on the phone required to install the application. Once copy protection is enabled, it cannot be disabled.)

I might need to change the name of the reader to remove this option.