I am developing a program to that only allows the same computer to view a specific page once, and after that I am blocking access to that page.
My question is, the IP address works ok but some users have a new IP every time they visit the site. I have come across other sites in the past that use some other means of tracking users, as even with a different IP on the same computer I can't view restricted content.
Anyone have any thoughts?
What are the other option(s) to the IP Address?
There isn't one method that you can use to be unique to any one computer.
You can set a cookie on that browser, but the user could use another browser or just delete the cookie.
There are 3rd party services that run a flash module to get computer specific data to create a guid that you can use, but that's more expensive and also requires the user to load your flash module, which means it wouldn't work on some mobile browsers.
The best you can do is tie up the functionality to a user account. That way, you have control over what the user sees.
Tying up to a machine isn't reliable.
Basically, a user has all the freedom to be free from your restrictions unless they opt to sign up with your service. That's what you call privacy as well.
And did you ever think when users share PCs? What if your dad got blocked on your laptop? You can't view it on your laptop anymore.
If the page is not public and sent to the user (ie by email), you can generate the URL with an ID, and them invalidate the ID once that the page is visited.
This is the usual approach used by email validation pages.