Blacklistbased

Blacklistbased refers to systems and policies that rely on maintaining and consulting a list of disallowed entities to block or restrict actions. In a blacklistbased approach, decisions are driven by whether an item appears on a precompiled blacklist, rather than by evaluating each item from first principles or relying on broader risk signals. Blacklists can target users, IP addresses, domains, content patterns, or applications.

Common applications include email spam filtering, where DNS-based blackhole lists (DNSBLs) are used to block messages from known spam sources; web content filters that prevent access to flagged domains; and network access controls that deny connections from listed addresses. Blacklists are also used in software security, ad blocking, and incident response to quickly deny known malicious infrastructure or problematic actors.

Key characteristics include the existence of a centralized or distributed list, a process for updating entries, and a rule that triggers a blocking or restricting action when a match occurs. Blacklists can be static or dynamic, locally managed or shared across organizations. They may be curated by individual organizations, security communities, or commercial vendors.

Advantages of blacklistbased approaches include simplicity, fast decision-making, and the ability to block known threats with minimal on-device computation. Limitations include maintenance burden, potential for false positives, incomplete coverage, evasion techniques by attackers, and concerns about privacy and over-blocking. Because of these limitations, blacklistbased systems are often used in conjunction with whitelist-based, reputation-based, or machine learning–driven methods to improve accuracy and adaptability.