Microsoft Graph is the API layer that exposes Microsoft 365 work data to applications and services. It lets tools such as Copilot query content the signed-in user is allowed to reach, including email, chats, calendars, documents, and other tenant data. In practice, Graph is the bridge between an AI assistant and the organization’s stored information.
It matters because any security issue in this layer can become a data-disclosure problem instead of a classic malware event. If prompts, queries, or retrieved content are mishandled, an attacker may cause the assistant to surface information the user can access but should not have revealed through that workflow. Defenders focus on least-privilege permissions, tenant controls, audit logging, and data loss prevention, because Graph-based access can amplify both legitimate productivity and accidental leakage.