AI Agent Security Explained: Agents, MCP, Prompt Injection, and the AI Harness

AI Agent Security is quickly becoming one of the most important areas in cybersecurity. This post breaks down terms appearing across conference talks, vendor announcements, and industry discussions, including agent, harness, MCP, tool calls, tool responses, instruction hijacking, indirect prompt injection, prompt exfiltration, and tool misuse, that are often used without clear explanations.