In cybersecurity, 'modular' refers to software or malware designed with interchangeable components or modules. Each module performs a specific function, such as data theft, persistence, or spreading to other systems. This architecture allows attackers to easily update, replace, or add new capabilities without rewriting the entire codebase. Modular malware is especially dangerous because it can adapt to different environments and evade detection by security tools. By mixing and matching modules, cybercriminals can customize attacks for specific targets, making defense and analysis more challenging for security professionals.