Your customer clicks on your payment button and are taken to PayPal's site for payment. Once they have completed their payment, PayPal sends an Instant Payment Notification (IPN) to the script on your site which verifies the payment, then sends them an email with their purchase attached.
E-paymentsoftware allows you to sell digital goods and offer instant downloads to your customers. After they have made payment the website will automatically email them the link to instantly download their purchase. The whole system is fully automated. This is the fastest way to sell non tangible goods on the Internet!
Since now you had several disavantatges:
Your customers share download your links, then their friends steal your files! You loose money and sales because you can't protect your files!
Automation was extremely expensive.
You had to wait to the payment transaction.
Your files are kept in an undisclosed folder, with undisclosed file names. The directory may be password protected, or you can set the permission of the directory, to insure more protection against someone accessing your files. When the script receives the IPN from PayPal it runs security tests to insure you receive; (a) payment, (b) payment in the correct amount and (c) the payment is completed. Only after these have been successfully completed, the script sends the email.