I'm trying to get a well-informed and full picture of why one as a single person should worry about being tracked across sites and uniquely identified. The reasons I can think of are:

  1. Serving ads as tailored to the user as possible (and thus likely to end in a purchase).
  2. Governments who want to crack down on individuals they consider to do unwanted activity.

Are there other major reasons one would want to worry about tracking?

Part of the reason for asking is that it seems now near impossible to avoid being tracked even for true experts, so one wants to know the damage one inevitably faces with the current state of things.

  • I believe targeted ads are the only reason. Tracking across multiple sites allows to gather more information and therefore create more detailled user profiles compared to single-site-tracking. This, in turns, allows for better ad targeting. – Euphrasius von der Hummelwiese Feb 14 '19 at 10:32
  • There are many kinds of targeted content serving that have not the goal of getting the user to purchase something. – Bergi Feb 14 '19 at 12:22

Users are tracked because the collected information can be sold.

A major reason why data is collected from users is due to the simple fact that people will pay for the data. There are many companies that broker collected data, such as Intellius, to virtually anyone with a deep enough pocket. What buyers do with this personal information, however, is up to the buyers. Many use it to serve ads. Others use it to learn more about their target demographic. Still others may use it for private investigation, or in flesh search engines. And, of course, governments use it for surveillance.

  • Welcome to the information age, dear reader. Where data, any data, has value for the right buyer. And not all buyers are out to make profit out of the data. Some are in the business of making the others take a deficit. – Mindwin Feb 14 '19 at 16:19
  • This question has gained considerable interest, yet it's on hold. Can you tell me what's off-topic about it? Internet privacy seems to me as on-topic for this site as you can get. – forthrin Feb 14 '19 at 16:49
  • Sometimes the information isn't directly sold. A company like Google may benefit from monopolizing the data it has and will opt to exploit the data in house. If they sell copies of the data then they can't monopolize it. (There is no integrity or selflessness to this, despite PR. It just prevents competitors on the ad-selling end (no one else has Google's targeting capability) and on the data-selling end (copied data can be resold.)) – Future Security Feb 14 '19 at 17:00
  • @forthrin Because it's more of a business question than an infosec question. – forest Feb 15 '19 at 8:53

The simple yet complicated answer is Because of data.

In addition to what schroeder said (tracking users for a commercial optimization,profiling and targeted marketing...), by profiling you, a company can anticipate your needs and actions.

Today we hear that by allowing a company to track you, it helps in “personalizing” your browsing experience :) meaning that two users browsing the same website won’t see the same content. This point is quite interesting especially when it comes to social networks or medias, depending on their profiles, two users will be served different articles or different versions of the same article to convey a given message more effectively.See following article for example: How Covert Agents Infiltrate the Internet to Manipulate, Deceive, and destroy the reputations

Sometimes, tracking users helps to get enough statistics to improve product's - website - functionalities and performances, by tracking users companies gain insights into how their products are being used and above all (hopefully) pimping them to meet each user's requirements.

  • 1
    Personalising content is not necessarily a bad thing, but it can definitely be abused. The same goes for "insight". It seems like a fine line between what is "understanding your users" and "spying on your users". – forthrin Feb 14 '19 at 11:58
  • @forthrin The same is true for ads. Most people don't seem to remember anymore, but advertisement is actually also meant to serve the (potential) customers - give them information about a new thing they can buy. Personalized ads could in theory be a great boon to internet users. The main problem is that in practice, they're still poorly personalized and suck anyway :) – Luaan Feb 14 '19 at 13:19
  • @forthrin that's why I put the word between quotes, and as Luaan said the positive side of personalizing stuff is usually theoretical – Soufiane Tahiri Feb 14 '19 at 14:24
  • @Luaan: Very good point. And rather worrisome that if they still suck so much with the immense surveillance going on, just imagine how bad things would have to get to actually make advertising "good". – forthrin Feb 14 '19 at 16:52
  • @SoufianeTahiri I think the best examples of personalised ads were those like Amazon's own, especially for books - its recommendations usually had two or three books I was genuinely interested in. But that's so much above average ad quality it isn't even funny :/ – Luaan Feb 15 '19 at 6:46

I would re-focus your conclusion about ads to be more generic, and bring the question more closely aligned with security/privacy. Users are tracked across a single website, across multiple websites, and other places to gather data with which to make decisions about that one user or for all similar users. The "making decisions" part is one of the big issues that GDPR is meant to address.

One of those decisions is to enable efficient targetting of ads so that advertisers do not waste money on ads displayed to the wrong people. As the phrase goes, "to display the right solution to your problem at the right time".

But the data can be used to profile what features users use or do not use, or what sites users like to visit in combination to know which sites should be partnering.

The more data that is collected, and the more profiling is done, the more the sites can provide personalisation and thereby be more attractive services to individuals instead of making guesses across a large population.

The downside is that a lot of information about people can be inferred, even things that people would not expect could be inferred simply by visiting a website.

  • I've rephrased the question to be more open. – forthrin Feb 14 '19 at 12:07
  • @forthrin My answer still applies without modification. Data is collected in order to make decisions. Profiling behaviours across multiple sites provides richer data. even for "government tracking" – schroeder Feb 14 '19 at 12:11

Because it may have an advantage and an advantage gets you clients and clients pay money.

Assume you're an advertising company and try to sell a big website ads. Another company is doing the same, but telling them they tailor the ads using tracking. You better start tracking, if you want to sell something. This does not mean either of you have an advantage though tracking, but you probably are still better off if you do so.

The next is tracking without ads. This can make you money, because the advertiser buys information from you, so he can tell the big websites, that his tracking is better.

There is a whole market of tracking. Twitter lets advertisers target users by income. Does Twitter know your income? Do you think they infer it from a few short messages in your stream? No. They give your e-mail and phone number to other companies and buy information. And maybe some payment provide sold your income information to these companies, so Twitter can tie your pseudonym to an income.

When you run a website and someone offers you to include their tracker to get some money, you may sell your users to them. And if you are running an ad network, you may make a deal with a tracking company to get some additional money and information.


One reason to track people across sites is to follow the trail of what sites led to a successful purchase. People do research on purchases, and the sites they browsed to may have been important in making the final decision to buy.

These intermediate sites might be profitable places to advertise. More nefariously, these sites might be good places to spam with phony reviews or comments. That means a site that you relied on to provide honest reviews might not stay trustworthy for long.

Not the answer you're looking for? Browse other questions tagged or ask your own question.