How are computers identified across networks?

Question

IP addresses are assigned to computers when they connect to the internet and change depending on your location. However, I read that your computer also has an address that doesn't change. So, when you connect to the internet, your IP address is assigned by the network and your address of your computer is shown to the network as well? Is that how the government finds out or the network you are using can determine what sites you searched or what you downloaded?

What I was thinking was if your computer did not have an address, how could they locate your computer once you left the network and moved somewhere else? I'm sure that they are able to now and was interested in understanding how the government or someone can find a user's location when they connect to the internet.

Answer 1

You can be detected even using different network devices. If you connect from home using the Ethernet card, and on a Starbucks using the Wifi card, it's trivial to detect you.

Now how:

• Cookies: The cookies on every site you access are independent of the IP address of your computer. So if you accessed Google from home, and accessed again from Starbucks, Google knows for sure that it's you.

• Browser Fingerprinting: Your browser is almost unique. The sum of browser version, OS version, plugins installed and updated (or not) is almost unique, and even if you delete all the cookies, you can be more or less identified.

• Canvas Fingerprinting: For the same reasons of the browser fingerprinting, the canvas object on HTML5 have a few differences based on a lot of variables, so it's possible to detect you, even if you use a different network card, delete all cookies and use a VPN.

Don't worry about MAC address, it's an address that never leaves the local network and can be easily forged, faked or cloned. But your behaviour cannot be faked, as you type and mistype the same words, access the same sites and so.

Answer 2

The other address you are talking about is a MAC address, but that is only used at the local link level, not to communicate across the open internet. Only your IP address is used when talking across the internet, however there are other ways to track you.

For one, the manual way is to contact whoever has the IP address and ask who was attached at the time. Your ISP may be to see the MAC address of your computer (if you were directly attaching to the cable modem) in their logs for the time and any hotspots you connect at can tell the mac address of the systems connected to them. This doesn't provide reliable tracking though as MAC addresses are trivially spoofed.

Another, easier way to be tracked is through cookies and other information unique to your computer that is shared by the browser. There is a lot of information that most browsers expose that tell unique things about your computer such as what set of plugins and versions are available, what browser and OS you are using, possibly some other accounts that you have, etc. When gathered together, this information actually is pretty good at identifying you and is actually part of how advertisers track you across multiple websites and locations.

Answer 3

Computers (more precise: their network interfaces) have MAC addresses which isn't intended change (although they also can). It has a different format as the ip, and it is invisible outside of the providers network. State spying works otherway.

Practically they use multilayer watching: there are their spy boxes by the network providers, there are by the big hosting farms. And, they have access to all bigger cloud databases (google, facebook).

What maker their work so effective, is that these data - from very different sources - is collected by them and are stored and processed integrated.

Of course they know your ip too, if they want, but practically they don't need to even ask your provider to say it them. It is there in the google/facebook session log, which they can surely mirror.