A domain name system (DNS) ad blocker is a tool that prevents access to websites that display unwanted ads or contain malware or trackers. Using a DNS blocker is helpful for blocking access to a whole group of IP addresses, which comes in handy for parents who want to block access to entire categories of online content, for example. DNS ad blockers include AdGuard DNS, NextDNS, and Control D, but there are dozens more. NordVPN Threat Protection also includes a DNS filter that strengthens its ad-blocking capabilities.