Blacklisting
Blacklisting is a security and access control concept where specific items, such as IP addresses, users, applications, or files, are explicitly denied access or blocked based on a predefined list of prohibited entries. It operates on a 'deny-by-default' principle for listed entities, allowing all others by default unless they match the blacklist criteria. This approach is commonly used in cybersecurity, network administration, and content filtering to prevent malicious or unwanted activities.
Developers should learn and use blacklisting when they need to block known threats or unwanted elements in systems, such as preventing spam emails by blacklisting specific sender domains, securing web applications by blocking malicious IP addresses, or restricting access to certain software in corporate environments. It is particularly effective for addressing specific, identified risks where the list of prohibited items is manageable and well-defined, but it may be less suitable for dynamic or unknown threats compared to whitelisting.