Digital Download Anti-Theft PHP Scripts

Hi,

Seeking php Digital Download Protector scripts
to stop people from STEALING My .mp3 files and
.pdf files purchased from My site...

Currently, Customer purchases product using PayPal,
then, customer gets sent to login page to download
the product, but now, I'm constantly getting bombarded
w/ download access from people that have NOT Purchased
the products...

How can I Fix this?

What I'm looking for is the following procedure:
Customer clicks PayPal Button,
pays for product,
gets URL for product download page,
URL cannot be shared...
(Or expires w/ in short time range... )

Thanks,

:)