How to check if iPhone app was installed before?
<p>Is there a way to check if my app was installed before? My app should offer half a year free of its services. Expandable via In App Purchase. I want to prevent the user from deleting my app and just re-downloading it.</p>

<p>I know there is a way to determine if my app is already installed (updates) (e.g. via variables in the NSUserDefaults). But what if the user deletes it first?</p>
