Microsoft Copilot does not add a new hole in your data security. It shows you the holes you already have. Copilot answers from the files, emails, chats and meetings each person can already open, so a folder that was shared too widely three years ago is suddenly one question away from anyone in the company. Keeping company data safe in Copilot is mostly about cleaning up access, labeling what is sensitive, and agreeing on what never goes into a prompt.
Know what Copilot actually does with your data
According to Microsoft's privacy documentation for Microsoft 365 Copilot, prompts, responses and the data Copilot retrieves stay inside your Microsoft 365 service boundary, Copilot only surfaces content the signed-in user already has permission to see, and your data is not used to train the underlying foundation models. Those are vendor claims tied to the business and enterprise versions, so confirm them against Microsoft's current terms for your license. Consumer Copilot accounts are governed differently, which is the first reason to make sure staff sign in with their work identity.
Fix oversharing before you turn Copilot on
Because Copilot respects existing permissions, the real exposure is over-broad ones: sites shared with "everyone in the organization," old team folders nobody owns, links that were never set to expire. Microsoft's guidance for a secure Copilot foundation starts here, using Purview data risk assessments to find overshared sites that hold sensitive content. Start with the places that matter most, such as HR, finance, legal and client folders, and tighten access there before you widen the rollout.
Label what is sensitive
Sensitivity labels let you classify content and attach protection to it. Copilot honors that protection, and Microsoft documents that a user needs the right usage rights on a labeled file for Copilot to use it. Keep the label set small enough that people will apply it correctly, and use default or automatic labeling for the folders where it matters most, so protection does not depend on every person remembering.
Add data loss prevention for Copilot
Purview data loss prevention can now be applied to Copilot. Microsoft describes policies that stop Copilot from using files and emails carrying chosen sensitivity labels as grounding data, and policies that keep Copilot from responding when a prompt contains sensitive information such as identification or payment numbers. Check which of these features your license and your tenant include, since availability varies by plan.
Turn on auditing and give it an owner
Copilot interactions can be captured in Purview's audit and compliance tooling, which lets you see who asked Copilot what and which files it drew on. A log nobody reads only helps after an incident, so assign an owner and a cadence, and set retention to match your records policy.
Control who gets Copilot, and what it can reach
License it deliberately. Roll out to a pilot group whose access you have already cleaned, watch what surfaces, then expand. Review any connectors, plugins and agents that let Copilot reach outside Microsoft 365, and allow only the ones your security review has approved.
Write down what never goes in
Controls reduce exposure but do not replace judgment. Keep credentials and passwords out of prompts. Keep regulated or contractually restricted material out unless your agreements explicitly allow it. And treat every answer as a draft: a person should open the cited source before a claim reaches a client or a published page.
A short checklist
Confirm staff use their work identity. Review sharing on your highest-risk sites and fix the broad links. Define a small label set and apply it by default where you can. Enable Copilot DLP where your license allows. Turn on audit logging with a named owner. Pilot before rolling out. Publish the never-paste list and review it twice a year. If a vendor claim matters to a contract or a client commitment, read the current terms yourself, because plans and policies change.