Are website operators allowed to detect and block website content based on browser add-ons?
<p>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.</p>

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

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

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

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

<p>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?</p>

<p>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:</p>

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

<ol>
<li><p>Your browser announces that it's running something.  This usually takes the form of a modified <a href="https://en.wikipedia.org/wiki/User_agent#User_agent_identification" rel="nofollow noreferrer">User-Agent header</a>.  I'm not aware of any privacy laws that consider "Person A told me something" to be an invasion of Person A's privacy.</p></li>
<li><p>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.</p></li>
</ol>

<p>Is it discrimination?  Yes.  <a href="https://law.stackexchange.com/a/681/137">But not all discrimination is illegal.</a>  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.</p>

internet