How do you set an app so that only iOS4 users can download it?

I have an app that is released in the app store and can be used by 3.x and 4.x. We compiled it using base SDK Latest 4.2, and deployment target 3.0.

But now we've added changes that are 4.0 required (i.e. this app WON'T work if you are using iOS3.x), but we don't want to tick off any users who have 3.x

If I set the deployment target to 4.0, will thi开发者_运维知识库s PREVENT a user on iOS3.x from installing it, and thereby deleting their older but still working version?

The last thing we want is to do an update, and have a number of 3.x users get ticked because not only can't they use the app anymore, but they can't go back to the slightly older version.

Future downloaders can't be on 3.x Current downloads will be not deleted, on 3.x, but cannot get future updates.

However, if a user updates their apps through iTunes, they may lose the app in question as iTunes applies the update, and won't sync it back to their device.

The latter case is an unavoidable bug, though.