I fed Cloudflare, Quad9, NextDNS, and AdGuard the same malicious domains to see who actually stops them

Security-focused DNS services all make roughly the same promise. Point your devices at their resolver, and known malicious domains can get stopped before your browser ever connects to them. Cloudflare, Quad9, NextDNS, and AdGuard all offer some version of that protection, but I wanted to see how often they would actually stop the same known-bad hostnames.