title: How do I copy-protect my Java application?
body: <p>I want to sell my Java application using PayPal. When a payment is received, the customer is mailed a one-time download link to my application.</p>
  
  <p>My question is, how do I prevent people from sending the .jar file to their friends/uploading it on the internet? </p>
  
  <p>Obviously I need some kind of check in the application which only allows it to run on one computer. And that's another problem, I don't want a customer to have limitations on one computer, they should be able to run it at home and work etc.</p>
  
  <p>Maybe some kind of cd-key would do the trick? Is there any cd-key resources for Java out there? Or should i build my own algorithm? Here comes yet another problem, reverse engineering..</p>
  
  <p>Please help me solve this :)</p>