A modular RAT, or remote access trojan, is malware built from a core loader plus add-on components. The base implant establishes access, then downloads or activates modules for tasks such as screen capture, keylogging, credential theft, persistence, lateral movement, or exfiltration. Because capabilities can be added after infection, the same malware family can be reused against different targets without changing the initial delivery method.
This matters in cyber security because modularity reduces the clues defenders may see at first. A small first-stage loader can look less suspicious than a full-featured payload, while later modules arrive only when the attacker needs them. In real intrusions, defenders may notice new network beacons, unexpected .NET assemblies, or commands that pull extra functionality from remote infrastructure. Good defenses focus on endpoint behavior, process ancestry, code-signing anomalies, and blocked outbound connections to stop the malware before its modules expand the compromise.