How can I identify a particular computer on my website without cookies (just like Twitter does)?

Question

I'm looking to identify each computer that accesses my website independent of cookies.

I know it can be done because Twitter does it. Here's proof:

1. Reset a browser (no cookies, no cache, total reset)
2. Visit twitter.com
3. Note the value of newly added _twitter_sess cookie
4. Repeat Steps 1 - 3. Cookie _twitter_sess will have the same value as before
5. Change IP addresses
6. Repeat Steps 1 - 3. Cookie _twitter_sess will have the same value as before
7. Change Browsers
8. Repeat Steps 1 - 3. Cookie _twitter_sess will have the same value as before
9. Change User Agents
10. Repeat Steps 1 - 3. Cookie _twitter_sess will have the same value as before
11. Change Computers
12. Repeat Steps 1 - 3. Cookie _twitter_sess will finally be different

How can I do the same? I'd like to track individual computers that visit my site independent of them clearing cookies, or expiring cookies.

Answer 1

Sounds like Twitter checks IP addresses from the browser request headers, so you would need to implement something similar on the server side when your request comes in. For example, in Java:

How can I retrieve IP address from HTTP header in Java

Edit: A solution that doesn't rely on IP addressed in more detail here:

How do I uniquely identify computers visiting my web site?