Domain blocking is a control that prevents users from reaching a specific domain name through registry actions, DNS filtering, ISP-level filtering, or other network controls. The site may still exist on a server, but the name that people use to find it no longer resolves normally or is harder to access.
In cyber security, domain blocking matters because the domain is often the main entry point to phishing pages, malware delivery sites, illegal streaming services, and command-and-control infrastructure. Blocking can disrupt traffic quickly, especially when attackers rely on disposable domains or redirects. Defenders use it to slow abuse and protect users, while attackers respond by registering new domains, changing DNS, or using mirror sites. For this reason, domain blocking is effective as a friction tactic, but it works best when combined with takedowns, monitoring, and rapid response to lookalike domains.