title: PHP Script to block unauthorized users from accessing a page
body: <p>I have to code a page that will only allow users that click on a specific link to access that page.  I don't want people to be able to type the address directly into the address bar and have access.  Only from a specific page and a specific link on that page.  </p>
  
  <p>Security is important as it is for a product download.  </p>
  
  <p>Anyone know how I would do this in PHP?</p>