In this case, it's about Ad Blocker. I've noticed more and more websites blocking their content based on whether their visitors are using this add-on or not.

From their point of view, I understand it's their income from these advertisements getting in danger.

From the user's point of view, I understand it's not just some annoying advertisement, but sometimes real danger like Trojans or Viruses.

Whoever is right however, is not the question. The question is more related to the invasion of privacy.

Is a website owner really allowed to know what kind of add-ons or programs I'm using without my permission?

Is such an owner not in fact discriminating based on what a user is using on his/her computer? Even so when the programs or add-ons being used are completely legal?

2 Answers 2


You've really got two questions here: 1) "Is it an invasion of privacy to know that I'm using an ad blocker?", and 2) "Is it discrimination to refuse service based on what software I'm running?". Taking them in order:

Because of how HTTP/HTML works, there are essentially two ways for a server operator to know what software you are running.

  1. Your browser announces that it's running something. This usually takes the form of a modified User-Agent header. I'm not aware of any privacy laws that consider "Person A told me something" to be an invasion of Person A's privacy.

  2. They guess it based on the actions your browser takes. For example, if the website gets a request for a page, and the site's ad network does not get a matching request for an ad, the server deduces that the user is running an ad blocker. Since this is based on things that the server operator could reasonably be expected to be informed of, it isn't an invasion of privacy under any law I'm aware of.

Is it discrimination? Yes. But not all discrimination is illegal. In general, only discrimination based on protected categories (race, sex, etc.) is prohibited, and I can't imagine a jurisdiction making "choice of browser add-ons" to be one of those categories, not least because it's something the person being discriminated against can easily change.

  • Thanks for the explanation. I guess that in the end both parties have good reasons for their actions. Though neither are doing anything illegal, so it simply comes down to making choices. Allow yourself to be vulnerable and see the website, or avoid it all together and miss out the content. Either way. There's never a win-win situation.
    – icecub
    Jul 4, 2015 at 0:53

I would have to agree with @Mark in that there are two questions being asked.

1) Are websites allowed to detect what the browser is running (plugins, adblock, ect)?

They are allowed to detect anything that you as a browser tell them. Many sites back in the early 2000 would serve up different content for mobile users, firefox users, IE users, any other type of users. Many sites still do, but the web is moving to a tell me what you can do as a browser. Something that many people forget is that you are going to their server and accessing their data.

2) Is it illegal to serve different content based on if they are serving ads?

No, not at all. The reason is that you have the way you interacted with the website first.

A point to make and question, are you doing something wrong by having an ad blocker?

You are breaking their website intentionally by having an ad blocker on. A website has a right to protect themselves against an attack. Now, and ad blocker may not be an attack, but you are actually doing something against the website to deprive them of their money. In effect, when you add an adblocker, you are blocking someone's source of income.

It is a funny way to look at it. Assume the site uses a CPM for there ad revenue, and lets say normal rate is $1.00 / 1000 Page views. You spend some time on the site over the month and view 100 pages. You have deprived the site of $0.10 for that month if you did not have your ad blocker on.

It may not seem like that much, but If 5 percent of your users block ads, it's not a big deal. If 95 percent come, take your content, but block your revenue, it's a big deal.

  • Well as I said. It's not about who's right or wrong. Blocking ads just because they annoy you would be wrong. But ads tend to install tracking cookies, spyware or worse. One might ask if it's still so perfectly fine to ask your visitors to endanger themselves simply for your own income?
    – icecub
    Jul 5, 2015 at 12:49
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    -1 for the terrifying idea that whenever I randomly land on a website, they have a right to exploit my privacy automatically and execute code on my computer to assist in exploiting me for the purpose of making money. If the content is so precious, it should be behind a pay wall. If it's not, then it's just elaborate bait to lure unsuspecting users in so that 40 third party networks can execute a drove of tracking code on them in exchange for money. Let's not be silly and suggest that ads are just pretty pictures being shown by the poor guy trying to make a legit buck.
    – user900
    Jun 29, 2016 at 11:23
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    Please avoid using emotive words like "stealing", particularly when most people take that to mean "commit theft", and (certainly in England and Wales), viewing a web site with an ad blocker is most certainly not an offence under the Theft Act 1968. Aug 2, 2016 at 20:00
  • @MartinBonner In that case could you give me a better word to use. In effect, when you add an adblocker, you are blocking someone's source of income. I will happily add that instead of stealing
    – Jdahern
    Aug 2, 2016 at 21:04
  • I think the final sentence of your comment is good. Use that instead of the one with'steal' Aug 3, 2016 at 5:05

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