Yesterday I was searching DuckDuckGo for booking a vacation. I ended up reading a lot on one specific website. Today multiple websites show me Google banners from this specific website. Normally, I never look up websites for booking a vacation. I use DuckDuckGo on purpose, to prevent these kind of things. My question therefore is: how is this possible?

I'm 100% certain that I didn't accidentally Google something.

The website I was reading was this, if that helps.

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    I think some sites uses banner provided by google so that when you login with your google account google fetch your search history and replace banners llnks according to your search. Commented Oct 11, 2017 at 11:28
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    most web sites share notes with google about where you go and what you do, and google knows how you (likely) got there even if they don't use google webmaster tools like ads or analytics.
    – dandavis
    Commented Oct 11, 2017 at 11:29
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    I use an add blocker and a cookie/tracker eraser on my browser and I have never recieved anounces regarding previous searches or pages I have visited. They should be configurable so you can whitelist pages where you want your cookies kept after closing the tab.
    – YoMismo
    Commented Oct 11, 2017 at 11:44
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    DuckDuckGo protects searches, but it does not protect you when you visit the sites it returns. You need another layer of technology to protect you once you move on.
    – schroeder
    Commented Oct 11, 2017 at 12:04
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    See beacons. They track people's behaviour online. You can get plugins to block them (I used to have a plugin called Ghostery back when I used Chrome which did just that).
    – Pharap
    Commented Oct 11, 2017 at 15:56

7 Answers 7


Loading that page loads


The reason Google can track you is that the website shares details of your visit with them - in this case via loading Google JavaScript code for their ads service.

*To expand on this -

The Google ad code will use a cookie to track you. But even if it didn't there are browser fingerprinting mechanisms which in most cases can correctly identify a user's machine even after a full browser cache / history clear.

When you visit a site with ads a request is made to the ad providers server. This sends the ID associated with you to say "an ad on [x website] for [user y] is available. The ad providers nowadays often then real-time auction off the slot in 1/100th of a second - where potential advertisers computers can bid for the advert space.

The site you visited is djoser. Since djoser knows you looked at products on their site yesterday they know there is a reasonable chance you are considering buying something from them. So when you visit another site somewhere else, the ad slot on that other site is more valuable to djoser, and they bid higher than anyone else - hence why you keep seeing them.

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    I'd suggest on top of DuckDuckGo using a well regarded ad blocker (I use u-block origin personally) and a privacy add-on like the EFF's Privicy Badger. This will stop 99% of tracking.
    – Hector
    Commented Oct 11, 2017 at 11:43
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    Somewhat As would *.doubleclick.net. An ad blocker would handle all of this for you.
    – Hector
    Commented Oct 11, 2017 at 12:40
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    @ThomasYates - Nope. You can fingerprint browsers by pulling lists of installed fonts, add-ins etc. It works out to be surprisingly unique - have a look at amiunique.org/fp
    – Hector
    Commented Oct 11, 2017 at 13:47
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    @S.L.Barth: This is also known as the "I love phishing" option, since constantly having to login to every site you use will condition you as a perfect victim for phishing. Commented Oct 11, 2017 at 19:15
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    @Hashim Yeah but you get a lot more chances to screw that up. Commented Oct 11, 2017 at 20:55

While Hector's answer correctly explains how Google got to know the page you visited, the real answer to the OP:

How did Google know I looked something up?


They Don't

In fact, no one is telling Google what your search was: only the destination page is sharing information about your visit, which does not include your search query (because DuckDuckGo hides that).

Of course, Google's advertising services still target you with content that is relevant to the website you visited (to avoid that, follow Hector's good advices), but they don't know what you looked up on DuckDuckGo.

Also, please know that Google do get informed of the fact that DuckDuckGo sent you there (while, sorry for the repetition, they don't get to know what you searched for)

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    They may not know the exact search term. But they know that you came from a search on DuckDuckGo - on a search for "test" and clicking the test.com result I see in the request header "Cookie:DOAAuthReferrer=https%3A//duckduckgo.com/; DO.."
    – Hector
    Commented Oct 12, 2017 at 8:03
  • @Hector true, I'll add that Commented Oct 12, 2017 at 8:04

It is most likely due to the website using Google tools.

Many website uses Google analytics or advertisement service, with whom they can get information on who's visiting their website etc.

Hence, Google is informed of your visit of this website.

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    And how can I prevent this? Because then using DuckDuckGo doesn't even make sense.
    – P.Yntema
    Commented Oct 11, 2017 at 11:34
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    See my answer. Using DuckDuckGo helps with sites that don't have advertising arrangements. Ultimately the only way to stop yourself being tracked is to use an ad-on that wipes all local storage on leaving a site and does things like randomise lists of presented fonts/add-ons to confuse fingerprinting attempts.
    – Hector
    Commented Oct 11, 2017 at 11:37
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    Google Analytics tends to be much more privacy-conscious. This is from several years ago, but the cookies it drops off are actually for the non-Google domain. Anything Doubleclick or Adwords related is a different story. Commented Oct 12, 2017 at 5:01
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    @MooingDuck - not at all. Look up EverCookie - any local storage available to a site an be used to store information to identify you for tracking purposes.
    – Hector
    Commented Oct 12, 2017 at 7:59
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    @P.Yntema Using DuckDuckGo does make sense, because DuckDuckGo doesn't keep track of who you are and what you have been searching for - as Google does. Just searching for something with Google, may result in customized ads (from Google) later... But more importantly, Google will make a profile over you, containing everything you've searched for. However using DDG doesn't mean your surfing anonymously - nor does it mean that the sites listed by DDG all will respect your privacy or that they don't contain ads with trackers. Commented Oct 15, 2017 at 18:57


@Hector already mentioned the reasons how it is showing related pages of your searched for last time. I would like add few more points. Well this is part of targeted marketing and their are many companies which are adding these google tags or other DMP tags like AdeX, KRUX, Salesforce, etc to the websites. So not only google is targeting you but also all these trackers from other DSPs(Demand Side Platform) or DMPs(Data Management Platform).


If you want to check on a website what trackers are present and if you want to manage them then you can use chrome extension called Ghostery or alternate softwares like Ghostery. You can block a specific tracker if you don't want to share your information with them. This is going to greatly reduce the advertisements related to your search.

By Ghostery, block all trackers you want to

  • thanks for adding alternates to a specific extension - it sort of looked like an ad for Ghostery
    – schroeder
    Commented Oct 13, 2017 at 13:27
  • @schroeder Yes thats what I realised and gave alternatives
    – Actung
    Commented Oct 13, 2017 at 13:48
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    Ghostery itself is a tracker.. If not disabled then, among other things, this information is collected: standard web server log information like your web request, the data sent in response to that request, a timestamp for the request, page And this information is always collected: web browser, operating systems, and opt-in settings to share Tracker information with the Company, when an installation, upgrade, or uninstallation occurs, and whether the GBE is active or engaged by you. (VI + VII in the privacy policy)
    – Andreas
    Commented Oct 14, 2017 at 15:42
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    Upvoted for good explanation of third-party tracking and how users can protect themselves. I had been using Ghostery for a couple of years but due to privacy concerns, I switched to the EFF's Privacy Badger. Instead of using a preset list of trackers, it continuously analyses third-party requests to determine whether or not they're tracking you. It's been working well for about 18 months and encouraged me to donate to the EFF. Commented Oct 16, 2017 at 12:24

This sounds like a remarketing cookie to me. Google, Facebook, and many other sites use "retargeting" (which Google calls remarketing) which gives advertisers the ability to target you specifically, on other unrelated sites that also serve ads in the same network.

So you visit site A about travel, and you read a few pages. Even if that site displays not a single ad, they can hit you with a retargeting/remarketing cookie. Now you go to site B, which is utterly unrelated to travel - say it's a TV show site - and they advertise using Google's Adsense program. If Google's algorithms determine that it is likely to be more profitable for them to show you ads for the travel site you visited previously, than to show you other ads for other things, then they will show you the travel ads.


Another possibility: https://superuser.com/questions/1250944/how-can-this-website-reidentify-me-even-after-deleting-all-of-my-browsers-histo

There is a little known area where sites can store informations in Firefox: the IndexedDB

To paraphrase the top answer from @arjan : They can store information inside IndexedDB (which is NOT cleared when you clear cookies, history, etc). To clear it you need to do something specific: either go to: about:permissions, or if it does not work (ex: Firefox 55), going into Tools, Page Info, Permissions to get the button "Clear Storage"

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    IndexedDB is in most major browsers these days and is normally part of a "clear application data" option in the clear history checkboxes. Its also not little known - its regularly used by web applications.
    – Hector
    Commented Oct 12, 2017 at 15:24

If your travel site sets a third-party cookie on behalf of an ad network the ad network can follow you around the Internet with knowledge of your previous behavior. Disabling third-party cookies can protect your privacy and prevent ad networks from collecting broad information about your behavior. With third-party cookies blocked, sites cannot set or read cookies on behalf of others and only the site that sets the cookie will have access to it.

You can this in Firefox under: Preferences - > Privacy and Security -> History -> Use custom settings for history -> Accept third-party cookies -> Never

Anyone who cares about online privacy should make this change in all their browsers on all their devices.

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