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How to get the real IP address of someone using a proxy?

I stumbled upon a government linked company website. There is support form in the website.

The website warn me not to submit joke or use other people's identity in the submit form.

They told me that even I'm using proxy, they still can trace... and lots of people has been traced.

I just wonder what kind of proxy that they can trace?

How about lots of website that offer proxy surfing (surfing anonymously)?

As a web developer that dont have experience in proxy, I cannot imagine how someone can trace people behind proxy

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marked as duplicate by Moab, Tom Wijsman, slhck, Sathya Apr 24 '12 at 5:58

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Fear is a powerful weapon (so, they might joke), other than that it depends on how anonymous you are.

Figuring out where the end point is (the IP they see), is trivial; that can be done with a tracert to it. Then the following logical step is to contact the ISP of the hops and request assistance, gathering its logs and/or connections. Not all ISPs do it, it kind of depends on the laws of the countries the hops belong to.

If they keep repeating it, they could find every hop from the end point to eventually you; only if it is clear that the connections leading to you are the ones they are after. This is where encryption and other nasty techniques which I will not enumerate upon here come into play, in essence they make it confusing to see from which connection certain packets came. Whole such networks do exist.

There are of course other techniques which either involve you (in)directly sharing stuff between the anonymous world and the real world, if a link can be made between both it takes away your anonymity.

So, if you are using the most basic approach (a proxy), it kind of depends how they route your packets further. If they do it straight (which is often the case to obtain higher speeds) and you use it illegally, you can be pretty sure that you are not as anonymous as the proxy claimed you to be. Even if you are really secure, you should still even consider not to play a joke on the government; that's simply unacceptable and even if they can't catch you, they will try to get as far as possible...

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Its not so easy. But they could

  • Look at the proxy logs
  • setting cookies in your browser and identify you when you re not using the proxy
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