Just because you’re paranoid doesn’t mean you’re not being watched.
When you’re on the Internet, there are good reasons to have that eerie sense of being followed.
By now, most of us know that websites can gather a surprising amount of information about your computer. For example, the page request you send to a site’s server includes detailed information about your browser — not just which browser you’re using, but the exact version, its configuration, and even the screen resolution the browser is running in. Other gathered data includes the page you came from, what document you’re requesting, and — yes, your IP address.
And don’t think you have anonymity just because your service provider gives you a dynamic IP address. At a minimum, visited websites can tell what service provider you’re with and what city or region you are in.
What’s more, any communication with a Web server gives it the opportunity to deposit a cookie on your computer. Benign cookies — small text files downloaded through your browser — simply record information needed to make your Web experience better. That can include sign-in information, where you visited on the site, interface customizations, and the like. Most cookies also keep an identifier for each visitor, so that the next time you connect to a site’s server, it can match you up with its records of previous visits. That way, you won’t have to start from scratch whenever you go to the site.
Less benign cookies can let websites track your movements around the Internet, and they often collect more information than you really want to give.
Typically, the information gleaned by trackers doesn’t include your name and street address. But by putting together all the collected data from page requests and cookies, Web servers can effectively fingerprint individual computers and thus track users across the Internet.