TL;DR: Multi-agent systems let AI components coordinate at machine speed, but every new agent and peer connection expands your attack surface. Layered defensive architectures — combining runtime inspection, secure protocols, and hierarchical structuring — are essential for maintaining visibility and preventing cascading compromise. This guide covers the frameworks, benchmarks, and implementation steps to build that defense correctly from day one. Multi-agent systems (MAS) let AI components coordinate at speeds and scales no human team can match, but that same speed creates network security risks that most teams discover too late. The attack surface grows with every new agent you add: each peer connection, tool call, and message hop is a potential entry point. Layered defensive architecture for multi-agent security requires visibility into agent behavior, intelligent runtime policies, and pre-execution defense that inspects prompts, outputs, and tool calls before a cascading compromise can take hold.…