Microsoft 365 Copilot is an AI assistant embedded across M365 applications that can summarise emails, draft documents, search across SharePoint, and answer questions based on data in the tenancy. Its capability derives from broad access to content the user has permission to see. That same breadth creates security and governance considerations that should be addressed before deployment.
The Oversharing Problem
In many Microsoft 365 tenancies, SharePoint and Teams permissions have accumulated over time without deliberate design. Files shared "with everyone" for convenience, sites accessible to the entire organisation by default, and broad group memberships mean that a user technically has access to data they would never actively seek out. Copilot surfaces this data proactively — making the effects of accumulated oversharing visible in a way that creates both productivity benefits and disclosure risk.
Access Control Remediation Before Deployment
The recommended preparation for Copilot deployment is a SharePoint access review: identifying overshared content, applying principle of least privilege to site and library permissions, and using Microsoft Purview sensitivity labels to classify and govern sensitive data. This is work that should have been done regardless of Copilot — the AI tool simply makes the consequences more visible.
Data Classification
Sensitivity labels in Microsoft Purview allow data to be classified by sensitivity level, with policies controlling what Copilot can do with labelled content. Highly confidential documents can be restricted from Copilot summarisation. This requires a data classification program — labels defined, policies written, and content labelled or auto-labelled — before the controls are effective.
Can Copilot expose client confidential data to other clients?
If a user has access to data from multiple clients and that data is not properly segregated with permissions, Copilot could surface it in responses. A proper client data segregation model — each client's data in a dedicated site with access restricted to the team serving that client — prevents cross-client data exposure. If you are in professional services and considering Copilot, this is the first question to answer.
