An ad blocker is software that stops online ads, trackers and pop-ups from loading in a browser, app or across a whole network.
How ad blockers work
Most ad blockers use community-maintained filter lists such as EasyList and EasyPrivacy. They block requests to known ad and tracking domains and hide page elements with cosmetic CSS rules. There are three common types:
- Browser extensions – for example uBlock Origin or AdGuard. Chrome’s move to Manifest V3 limited how powerful extensions can be, so blocking now works through declarative rule sets.
- DNS-level blockers – Pi-hole, AdGuard Home or filtering DNS resolvers block ad domains for every device on a network.
- Built-in protection – browsers such as Brave, Firefox and Safari block many trackers by default.
Why ad blockers matter for security
Ads are not only annoying. Malvertising – malicious ads in legitimate ad networks – regularly pushes fake software downloads, tech-support scams and phishing pages, and search ads imitating popular programs are a known way to spread stealers. Blocking ads and third-party scripts reduces this attack surface and limits tracking of your browsing.
At the same time, fake ad blockers are a classic lure: extensions with names similar to well-known tools have been caught injecting ads, hijacking searches or stealing data. An extension with permission to “read and change all your data on all websites” sees everything you do in the browser.
Best practices
- Install only well-known, open-source blockers from the official browser store and check the publisher.
- Keep the number of extensions small and review their permissions.
- In companies, consider DNS filtering on the network level instead of letting users install random extensions.
