What is adblock?

Sander van Hezik 1 Sep 2020

Adblockers play a key role in protecting our privacy and providing a smooth browsing experience

Technically speaking, adblockers do not block ads – they block web requests that download content into the browser. In other words, adblockers stop ads from downloading on your browser, allowing web pages to load faster and offering a better browser experience.  

Further reading: Should you use an ad blocker?

How does Adblock work?

Adblock technology relies on simple lists, called filter lists, that determine what to block and hide, or what to allow to appear on the pages you visit. These lists simply consist of a list of URLs in the form of either an “allowlist” or “blocklist”.

When you visit a website, adblock quickly checks if that website is in one of these filter lists. If it is, then the request to external content is blocked and the ad is not downloaded into the webpage. In a nutshell, adblock technology is a set of rules that are established in these filter lists that determine what should be blocked or not blocked on webpages you are visiting. 

Filter lists are typically maintained by a third party community that is not affiliated with the developers of adblockers or ad companies.

Examples of filter lists

  • EasyList: A huge blocklist collection of URLs of known ads on English-language websites all over the web. The goal of this blocklist is to automatically remove any type of unwanted content that doesn’t belong on the webpage, such as plain, unformatted images and web page designs that are not part of the actual website, pop-up ads and banners, auto-playing videos with sound that cover half your screen, strange tracking, and so on.
    • It is maintained by the community (in other words, it’s largely unbiased).
    • Sometimes, some ad content is preloaded to the website, which the adblock technology cannot block it from loading. In these cases, Easylist is telling the adblock technology to hide that unwanted content, so it doesn’t appear on the web page.
  • EasyPrivacy list: Exactly the same as EasyList, just for non-English websites. In addition, it also blocks some social media buttons and in-page pop-ups (for example, sponsored content on Facebook).

  • Acceptable Ads Standards filter list: This list is an allowlist and was developed based on user feedback from actual adblock users. It is managed and sponsored by the company Adblock Plus. These standards aim at creating the best type of ads in order to improve and optimize the user experience while browsing the web. 
    • The Acceptable Ads allowlist is usually enabled by default when you install an adblock extension.
  • Local list: An allowlist that is created by you either by adding a web address in the settings pages of your browser or by allowing them within the adblock app.

  • Any other custom list: The Avast Partner allowlist, for example, allows “search” type of content to appear while you browse the web. Such are search results when using a search provider (Google, Bing, Yahoo, etc.), or shopping online (Amazon, Facebook Marketplace, etc.).

How are ads used?

The short answer is that companies use ads as part of their marketing or promotional activities to introduce their offerings to users, and thus, drive sales and overall revenue. Advertising plays a different role at different stages of that marketing process that enables a company to raise awareness of a product or service.

Without ads, we wouldn’t be able to buy our favorite products or brands, access on-demand services or make our dream vacation a reality. 

Benefits of ads

Ads should benefit both sellers and consumers. As previously mentioned, companies can promote their offerings through ads. On the other hand, consumers can access the necessary information around the available offerings, discount deals, and other potential options available in the market in order to make informed decisions. 

Why are ads a problem?

There are multiple reasons as to why ads are unwanted and perceived as a negative thing.

First and foremost, ads have become an exaggeration of reality. Second, user preferences and needs have evolved in such a way that ads need to not only represent the reality and truth, but they must also be intuitive, relevant to one’s wants and beliefs and placed on the right channel at the right time.

Unfortunately, ad creators tend to be more focused on just attracting the eye of a consumer rather than create engagement. This has resulted in highly disruptive ads, annoying ads, ads that provide a very bad experience to the user. Continuing along this line, the majority of ads are so heavy for a webpage that websites tend to take a much longer time to load, creating a bad browsing experience.

Thirdly, some ads also utilize tracking and behavioral monitoring technology that profiles user behavior based on the websites they visit by downloading files on people’s computers. These methods can easily be exploited by external attacks in order to gain access to users’ sensitive information leading to identity theft, and so on.

To conclude, ads today are perceived as an invasion of privacy and a security risk. Ad creators and ad platform providers need to come up with smart ways in placing the right ad at the right time at the right channel and ask permission before activating any tracking and monitoring technology.

How to fight against ads 

As advertising platforms continue to utilize tracking and behavioral monitoring technology, content blockers and adblockers become more of a trend and a need in order to protect our privacy and have a better and smoother experience when browsing the web.

However, adblockers might not be the answer. At the end of the day, we all want to have highly personalized content provided to us that is based on our personal preferences and needs. In order to do so, companies need to be able to access information in order to create highly customized content and products. However, companies need to respect the consumers and come up with non-disruptive and non-intrusive ways when accessing our information, without invading one’s privacy.

Some companies have tried to deal with these issues and controversies and have developed several agreements around the creation, format and placement of ads. There are two well known committees: The Acceptable Ads Standards Committee (AAC) and the Coalition of Better Ads (CBA).

Ad standards and agreements

Acceptable Ads Committee

Acceptable Ads is an initiative that was launched in 2011 by Eyeo, the company behind Adblock Plus. The initiative aims to improve the digital advertising ecosystem and make it more sustainable. The criteria for Acceptable Ads was initially developed by Eyeo in 2012 with a little bit of input from users of Adblock Plus. However, the initiative was then handed over to the Acceptable Ads Committee (AAC), which was established in 2017.

  1. For-profit coalition: Includes business stakeholders, advertisers, ad-tech providers, advertising agencies, publishers and content creators.

  2. User Advocate coalition: Includes general stakeholders, such as ad-blocking users and digital rights organizations. 

  3. Expert coalition: Includes stakeholders that are specialists in online advertising and ad blocking, such as researchers, creative agents, user agents and academics.

The AAC has developed and improved upon the initial CBA criteria, which are adhered to by members of the ecosystem in order for ads to be considered as less invasive and annoying. The AAC has identified 3 main categories of “acceptable ads”. 

  1. Placement: Ads must not disrupt the user’s natural reading flow. They should be placed above, below or beside the main content. 

  2. Distinction: Ads and content should be clearly distinguishable and must be labeled as an advertisement or its equivalent. 

  3. Size: The amount of space taken up by ads should never exceed content space. Ads should also comply with size limitations depending on the position.

Coalition for Better Ads

On the other hand, the Coalition for Better Ads was formed in 2016 by a number of trade associations and companies involved in the media (Google, Microsoft, Facebook, Unilever and the American Association of Advertising Agencies). 

The coalition was formed to understand consumers’ preferences and address their expectations within the digital advertising ecosystem. This is important, as the online business model is sustained by ads → online publishers depend on ads to fund their content creation in order for their users to access their content for free.

Unfortunately, the emergence of intrusive and disruptive ad formats, such as pop-ups and large sticky ads, frustrate the user and create a very bad browser experience, leading to a large increase in the number of users installing ad blockers.

The Better Ads Standards are based on extensive research, consumer insights and cross-industry expertise into the least preferable ad formats to identify which formats are most likely to cause consumers to install ad blockers.

The CBA identified 12 ad experiences that were considered by users as the least favoured and the most likely to prompt them to adopt an ad blocker

Some very known examples include auto-play video ads with sound (outstream), flashing animated ads and full-screen scroll over ads.


Key takeaways

The main difference between the two is that the CBA was developed by trade associations and companies involved in the media who carried out research to establish which ad formats to avoid in order to reduce the number of adblockers. Conversely, the AAC was developed through surveying adblocking users in order to establish which ad formats they deem as ‘acceptable’.

The sole purpose of both committees is to protect the user experience whilst also ensuring that publishers and ad creators are able to monetize their traffic sustainably, thus keeping content free. 

Possible issues with adblock

Although we discuss the negative aspects of advertising, it’s important to remember that adblock technologies also have negative aspects.

A strong adblocker might break some websites and disrupt the browsing experience. Since adblockers are blocking unwanted content found within websites, it might cause some inconsistencies and inability to access websites that contain cookies and other tracking methods. Good examples are Amazon.com, Google search, Bing Search, Yahoo.com, and so many other websites where we expect and sometimes demand from them to serve us relevant information and results based on our history and preferences.

Unfortunately, adblockers break this user experience that we all have become accustomed to. 

Another example that can be perceived as not that positive are social networks. Unfortunately, social networks don’t allow you to access their websites with an adblock turned on. Which leads to a whole other discussion and political debate around the power of social networks and how they have shaped our lives. 

Further reading: Should you use an ad blocker?

How does Avast Secure Browser protect me from ads?

At Avast, we strive to build relevant products for our users. Through the ups and downs, we are committed to creating one-of-a-kind products that will protect your privacy and provide you with a secure browsing experience across the web, without disrupting your browsing session.

Therefore we have a built-in adblock using the uBlock technology, and we are currently working on a new version of adblock which gives you even better protection to enhance your browsing experience.


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