Privacy glossary

Ad blocker


What is an ad blocker?

An ad blocker is a browser feature, or a browser extension, that prevents your Web browser from showing ads on webpages, videos, streams, podcasts, or apps. Ad blockers often improve your browsing experience, but can bring security risks.

Why use an ad blocker?

Ads on websites degrade your browsing experience in several ways. They create visual clutter (especially if they’re animated), and take up extra space on the webpage you’re viewing. They can cause webpages to load more slowly and consume more bandwidth. The extra processing required to display ads can even shorten your device’s battery life.

Ads are often bad for privacy as well. Ad networks (the tech companies that serve ads) track your browsing activity so they can show you ads you’re more likely to click on. These ad networks also keep track of which ads you see and click on.

What are the different kinds of ad blockers?

In general, there are two kinds of ad blockers: browser extensions, and “native” blockers (those built directly into the browser).

Ad-blocking extensions, like any other type of browser extension, come with privacy and performance risks. They’re made by third-party developers who may or may not be trustworthy. They might collect data about your browsing activity. And they might slow down your browser or drain your battery life. In other words, extensions can cause some of the same problems that ads do.

To mitigate these risks, some browsers limit what they allow extensions to do. However, that creates a different problem: With limited capabilities, extensions might not be able to do comprehensive, fully effective ad blocking. There’s a fundamental tradeoff between safe extensions and powerful extensions.

Native ad blockers—like the Brave browser’s Brave Shields feature—are built directly into the browser, so there’s no tradeoff: They can do powerful, flexible blocking without hurting privacy or performance.

How do ad blockers work? How do they know what’s an ad and what isn’t?

Ad blockers use lists of criteria, called “filter lists,” to identify parts of a webpage that contain ads. They look at characteristics of the webpage’s HTML, and of the URLs that content is loaded from. If a part of a page’s HTML matches an entry on a filter list, the browser hides that part. If the URL for a piece of content matches an entry on a filter list, the browser won’t load anything from it. Most ad blockers allow users to customize the filter lists they use.

A mostly-volunteer community builds and maintains filter lists, a largely manual process. They work to keep filter lists updated as the online environment changes (for example, when new ad servers come online). Given how complex the environment is, though, filter lists can’t be perfect all the time.

Are there types of ads that ad blockers can’t block?

Using filter lists to identify ad content means that some types of ads are hard or impossible for ad blockers to block. One important example is paid social media posts: when an advertiser pays someone with a large social media following to promote their products.

Another example is native advertising: articles on news sites or blogs that are designed to look like normal articles but were actually paid for by an advertiser. “Advertorials,” for example, are a type of native advertising.

Ads that are loaded from the same server as the webpage they’re on (first-party ads) can be difficult for ad blockers to distinguish from the page’s non-ad content. Ad blockers are sometimes more lenient on first-party ads, to avoid breaking the site’s other functionality. This type of ad mostly appears on sites from major tech companies, like Google or Facebook.

Do ad blockers ever deliberately let some ads through?

Some ad blocker developers work with ad networks (the tech companies that serve ads) to let some ads through, sometimes in exchange for payment. Though they usually impose conditions on these ads (as with Adblock Plus’s “Acceptable Ads” program), like requiring that ads be visually unobtrusive.

What’s the difference between an ad blocker and a tracker blocker?

Ad blockers and tracker blockers work similarly—preventing the browser from loading certain content, using filter lists—but they’re focused on blocking different types of content. Ad blockers are primarily focused on visible ads, sometimes without regard for whether those ads are tracking you. Tracker blockers are primarily focused on trackers (which are often invisible), and may not block visible ads that aren’t known to track people.

Most ads include trackers, though, so there is significant overlap between the two types of blockers. For example, if you use a tracker blocker, you’ll see fewer ads than if you didn’t use any type of blocker.

Can VPNs block ads?

Some personal VPNs offer ad blocking as a feature. VPN ad blocking tends not to work as well as in-browser ad blocking, because they can’t see and modify the content of webpages that you visit using HTTPS (which is most webpages). VPNs block ads by blocking traffic to known ad servers, which is a less precise approach. However, VPN ad blocking has an advantage: it can block ads in apps other than your browser.

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