Why do you get personalized ads on websites?

You bought a new pair of sports shorts a few days ago. And now advertising banners with a matching training jacket pop up on many pages. This can’t be a coincidence. What’s behind it?

“Personalized advertising, that’s ads that relate to who we are, what we’ve looked at and what we’ve used,” explains Rebekka Weiß from the IT industry association Bitkom. She describes a mechanism that almost every Internet user has experienced.

You look at a certain product and then all of a sudden it gets suggested on other websites. But how does that work?

Cookies play a role in personalized advertising

Certain tracking mechanisms are used on websites to store what people look at. Most often, this happens via cookies, small files that the browser stores. “Web servers can have the browser set a cookie when the visitor calls up one of their pages,” explains Jo Bager of the trade magazine “c’t.”

“Because cookies often contain unique identifiers, websites can recognize their visitors,” Bager summarizes. A distinction is made between first- and third-party cookies. The former are set by the visited website itself. If a site embeds content from other sites, these can also set cookies on the website: Third-party cookies. “Advertisers embed content everywhere on the web, that’s why they can track users everywhere,” Bager explains.

We are auctioned off while surfing

If you call up a page that offers a place for personalized advertising, a kind of auction starts. The advertising partner then automatically advertises information about the visitor, for example the (presumed) gender or (presumed) interests, says Bager. Advertisers can then bid on that information – whoever bids the most gets to show their ads to the visitor. “This happens within milliseconds, and the visitor doesn’t notice.”

So how transparent are we? And what information is being collected about us? “Technologically, it can be just about anything,” says Rebekka Weiß. The most relevant information in the advertising environment, she says, is that the user is interested in a particular product. If this user then calls up a series of articles, she says, it can be deduced, for example, whether someone has a particular interest in sports or outdoor activities.

“You can then infer hobbies, political interests, or even health information,” explains Weiß. Ultimately, of course, site operators and advertisers would have to comply with the requirements of data protection law and obtain the user’s consent in many cases. That’s what cookie banners are for.

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Users click “OK” too quickly

“The provider has to break down the purposes for which it collects data and with whom it is shared,” says Weiss. “But most users click OK without reading through the full information.” Many don’t give much thought to what they’re consenting to. Yet that’s exactly what’s important to make an informed decision, he says.

Hans-Dieter Neumann of the German Association for Data Protection e.V. (DVD) lists what websites and advertisers know about us: “They can tell what device I’m using, what browser and what operating system I’m using to go to the website.” Neumann explains that 99 percent of visitors to a website can be uniquely identified by these various characteristics of a device.

But how do we protect ourselves? Hans-Dieter Neumann advises, for example, that social networks should be used sparingly, with caution or, if in doubt, not at all. This is because people voluntarily disclose a lot of their data on social media, which makes it very easy for operators to create comprehensive, accurate profiles of users.

Jo Bager advises using the privacy options of the browsers and blocking third-party cookies and other tracking mechanisms, for example. He considers the Firefox and Brave browsers to be best positioned in terms of data protection. “As search engines, I would recommend Duckduckgo, Startpage or Metager for privacy-conscious surfing.”

Normal search engines cut in

Data protection expert Neumann is also not a fan of conventional search engines: “A normal search engine uses information about what you have previously searched for and selects the search results. However, if you use Startpage, for example, you can open Google content without information about your own device or search behavior being passed on.

Rebekka Weiß also has some tips: If you don’t completely deactivate the creation of a browser history, you can regularly delete cookies and search histories, for example. In addition, she says, there are many browser extensions that want to help better control tracking.

And with Google accounts, for example, it’s possible to remove information that’s being used for advertising purposes, says Weiss. “That’s done through the dashboard. I can view and delete my histories there. I can also set what is collected in the first place.” The dashboard can be found in the settings of one’s Google account.

Rebekka Weiß thinks it’s important for users to look into the issue and actively decide whether they want to care. Her conclusion: “Completely anonymous use of the Net is hardly possible, but you can at least control your data traces.”

In Jo Bager’s view, a kind of Wild West mentality has taken hold in the advertising industry, with companies grabbing hold of as much data as possible: “Consumers often don’t even know who has all the data about them. That’s why they should try to protect themselves as much as possible.”