Copilot Can See More Than You Think: Fixing Oversharing Before You Deploy

Microsoft 365 Copilot does not automatically give employees access to information they could not already open.

It works within your organisation’s existing Microsoft 365 permissions and access controls. However, that is exactly why poorly governed SharePoint sites, OneDrive folders, Teams workspaces and Microsoft 365 groups can become a serious problem during deployment.

If an employee already has unnecessary access to a document, Copilot may be able to find, summarise and reference that document for them.

Copilot has not created the permission problem. It has made that problem easier to discover.

Before assigning Microsoft 365 Copilot licences broadly, businesses should identify excessive permissions, remove outdated sharing, classify sensitive information and establish clear ownership for their SharePoint and OneDrive data.

This guide explains how to fix Microsoft 365 oversharing before Copilot turns years of forgotten access into instantly searchable business intelligence.

What Can Microsoft 365 Copilot Access?

Microsoft 365 Copilot can ground its responses in information the signed-in user is permitted to access across supported Microsoft 365 services.

Depending on the task and product experience, this can include information from:

• SharePoint Online
• OneDrive for Business
• Microsoft Teams
• Exchange Online
• Microsoft 365 groups
• Meetings, messages and calendars
• Files shared directly with the user

Copilot respects the underlying Microsoft 365 permission model. It does not independently grant permission to a restricted document or site.

The risk appears when existing permissions are wider than the organisation intended.

For example, an employee may technically have access because:

• “Everyone except external users” was added to a site.
• A department-wide security group was used for convenience.
• An old Teams workspace still includes former project members.
• A folder inherited permissions from a broadly accessible library.
• A user received a direct link years ago.
• A sensitive file was stored in a general-purpose site.
• A Microsoft 365 group was never reviewed.
• A OneDrive folder was shared too widely.

Before Copilot, the employee may never have known the document existed.

With Copilot, they may be able to ask a natural-language question that causes relevant information from that document to surface in the answer.

Why Copilot Changes the Oversharing Risk

Traditional Microsoft 365 access often depends on users knowing:

• Which site to open
• Which folder to browse
• Which search terms to enter
• Which document contains the answer
• That the information exists at all

Copilot reduces that discovery burden.

A user can ask:

What are the planned redundancies for next quarter?

Or:

Summarise the proposed acquisition and the financial risks.

If the user has access to an overshared HR, legal or finance document, Copilot may use that content when producing its answer.

The concern is not that Copilot bypasses access controls.

The concern is that it makes authorised-but-inappropriate access faster, easier and more useful.

The Difference Between Access and Business Need

A user can have technical access without having a current business need.

This often happens because permissions accumulate over time.

An employee may retain access after:

• Changing department
• Completing a temporary project
• Leaving a management role
• Moving away from a customer account
• Finishing work with a supplier
• Joining a site for one document
• Being added through a large security group

Copilot evaluates what the account can access, not why that access was originally granted.

Your pre-deployment review should therefore ask:

Should this person still be able to use this information?

Not merely:

Does Microsoft 365 currently permit access?

Common Oversharing Problems to Fix

Organisation-Wide Access on Sensitive Sites

SharePoint sites sometimes include broad groups such as:

• Everyone except external users
• All employees
• Large department-wide groups
• Large dynamic Microsoft Entra groups

That may be appropriate for policies, templates and general company information.

It is rarely appropriate for:

• Payroll
• Employee relations
• Legal disputes
• Board papers
• Acquisition planning
• Security investigations
• Customer financial records

Sites with large numbers of users pose a greater risk of unintended exposure through Copilot interactions.

Old Microsoft Teams Membership

Every standard Microsoft Team has an associated SharePoint site.

Users added to the Team may gain access to files stored in that workspace.

Review Teams created for:

• Completed projects
• Old customers
• Recruitment exercises
• Restructuring
• Legal matters
• Supplier evaluations
• Incident response

Remove members who no longer require access and archive or delete workspaces that no longer serve a legitimate purpose.

Uncontrolled OneDrive Sharing

OneDrive is designed primarily as an individual user’s working area, but it often becomes an unofficial business repository.

Risks include:

• A manager sharing a large folder with an entire department
• Sensitive content remaining accessible after a project
• Former employees’ data being transferred without permission review
• Long-running collaboration that should have moved to SharePoint
• Anonymous or broadly accessible links

Long-term departmental content should normally be moved into a managed SharePoint site with defined ownership and access controls.

Broken Permission Inheritance

A document library, folder or individual file may have unique permissions that differ from its parent site.

Unique permissions can be legitimate, but they are difficult to manage at scale.

Investigate locations where:

• Many items have separate permissions
• Nobody remembers why inheritance was broken
• Direct access has accumulated over several years
• External users remain attached to individual items
• Sensitive files sit inside broadly available folders

Anonymous Sharing Links

Anyone links can allow a file or folder to be opened without authenticating as a named user.

These links create a different risk from ordinary Copilot grounding because Microsoft 365 Copilot operates in the context of an authenticated user. However, anonymous links still indicate weak data governance and may expose the same sensitive content outside the organisation.

Before deployment:

• Review and remove old Anyone links.
• Configure expiration periods.
• Use Specific people as the default sharing option where appropriate.
• Restrict anonymous links to view-only access when they are genuinely required.

Start With an Inventory of Your Data Estate

You cannot remediate oversharing without knowing what exists.

Create an inventory of:

• Active SharePoint sites
• OneDrive accounts
• Microsoft Teams workspaces
• Microsoft 365 groups
• Site owners
• Sensitivity labels
• External-sharing status
• Last activity date
• User and group counts
• Business purpose
• Data owner

Prioritise sites that are:

• Highly populated
• Externally shared
• Unlabelled
• Ownerless
• Inactive
• Connected to sensitive departments
• Using broad organisation-wide permissions

Use SharePoint Data Access Governance Reports

SharePoint Data Access Governance reports can help identify sites containing potentially overshared or sensitive content.

Available reports may help assess:

• Site permission states
• Sharing links
• External access
• Sensitivity labels
• Broad user access
• Permission changes

A practical review process is:

1. Open the SharePoint admin centre.
2. Go to Reports.
3. Select Data access governance.
4. Review available snapshot and activity reports.
5. Identify sites with the broadest access.
6. Assign owners to investigate them.
7. Record remediation decisions.
8. Repeat the reports regularly.

Some capabilities may require SharePoint Advanced Management or suitable Microsoft 365 licensing.

Run Site Permission Reports

A site-permissions report can show how broadly SharePoint and OneDrive locations are exposed.

Use it to identify:

• Sites accessible to very large groups
• Sites with many direct permissions
• Sites with external users
• OneDrive locations with unusually broad access
• Sensitive sites lacking restricted membership

Do not assume that a high user count is always wrong.

A company intranet may legitimately be available to everyone.

The question is whether the audience matches the information stored there.

Delegate Reviews to Site Owners

Central IT may be able to identify a site with 300 users, but it may not know which 40 genuinely require access.

Site owners are often best placed to decide:

• Which users are still active
• Which groups are too broad
• Whether a project has ended
• Whether files should be archived
• Whether external access is still required
• Whether the content belongs elsewhere

Every review should result in a recorded decision:

• Access confirmed
• Users removed
• Group replaced
• Sharing link deleted
• Site restricted
• Content moved
• Site archived
• Escalation required

Avoid sending site owners a spreadsheet and simply asking them to “check the permissions.”

Give them a clear deadline and decision framework.

Fix Broad Group Membership

Large groups are convenient, but they are also one of the most common sources of oversharing.

For each broad permission, determine:

• What business purpose does it serve?
• Does every group member need access?
• Is the group actively maintained?
• Is membership based on reliable employee attributes?
• Are former employees or contractors included?
• Could a smaller role-based group be used?

Replace vague groups such as:

All Managers

Project Users

Operations Access

Shared Documents

With clearly governed groups such as:

Finance Payroll Approved Users

Legal Employment Cases Team

Project Phoenix Active Members

Board Reporting Authors

Each security group should have:

• A named owner
• A documented purpose
• A membership-review schedule
• A removal process
• An approval process

Use Restricted Access Control for Sensitive Sites

Restricted Access Control can limit a SharePoint site so users must meet two conditions:

1. They already have permission to the site or content.
2. They belong to a specified Microsoft Entra security group or Microsoft 365 group.

Adding a user to the restricted group does not grant access by itself. It creates an additional access boundary around the site.

This can be useful for:

• Executive leadership
• Payroll
• Legal matters
• Cybersecurity investigations
• Acquisitions
• Board documents
• Highly confidential customer projects

Restricted Access Control changes actual site access, so test it carefully before enforcement.

Use Restricted Content Discovery as a Temporary Guardrail

Restricted Content Discovery can reduce the chance that content from selected SharePoint sites appears in organisation-wide search and Microsoft 365 Copilot while the site is being reviewed.

It may be suitable for:

• High-risk overshared sites
• Sites undergoing permission remediation
• Phased Copilot deployments
• Sites awaiting ownership confirmation

However, it does not remove existing permissions.

Users who already have direct access can still open the content, and recently accessed or owned content may remain discoverable in certain circumstances.

Use it as a temporary safety measure—not as a replacement for permission cleanup.

Applying it too broadly can also reduce the completeness and usefulness of Copilot and search results.

Do Not Treat Restricted Search as a Permanent Fix

Restricted SharePoint Search and similar discovery controls can help during a controlled rollout, but they do not repair underlying access.

Users may still be able to access:

• Content they own
• Content they recently used
• Content they can open directly
• Information available through permitted sites

The long-term solution remains:

• Correct permissions
• Appropriate group membership
• Content classification
• Site lifecycle management
• Access reviews
• Monitoring

Apply Sensitivity Labels to Sites and Content

Microsoft Purview sensitivity labels can help users and administrators understand how information should be handled.

Labels might include:

• Public
• Internal
• Confidential
• Highly Confidential
• HR Restricted
• Legal Privileged
• Finance Restricted

Sensitivity labels can apply protection to individual files and emails. They can also govern containers such as Teams, Microsoft 365 groups and SharePoint sites.

Container labels may control settings such as:

• External sharing
• Privacy
• Unmanaged-device access
• Guest access

However, labels are not a substitute for correct permissions.

A document labelled Highly Confidential is still overshared if hundreds of unnecessary users can open it.

Use labels and permissions together.

Configure Data Loss Prevention

Microsoft Purview Data Loss Prevention can detect sensitive information and respond when users share or move it inappropriately.

For Copilot readiness, DLP policies can help protect content involving:

• Personal data
• Payment-card information
• Bank details
• National identification numbers
• Medical information
• Confidential business records
• Intellectual property

Possible actions include:

• Audit
• Warn
• Require justification
• Block external sharing
• Generate alerts

Start DLP rules in simulation mode and tune them before blocking activity.

The goal is to identify meaningful oversharing without burying users and administrators in low-value alerts.

Review External Sharing

Copilot deployment should not distract from traditional external-sharing risk.

Review:

• Anyone links
• Specific people links
• Existing guests
• External site members
• External Teams users
• Domain restrictions
• Link expiration
• Anonymous edit links

Set external-sharing levels according to the site’s purpose.

Clean Up Stale and Ownerless Sites

Old sites contribute to both data sprawl and oversharing.

They may contain:

• Outdated reports
• Draft contracts
• Old employee information
• Historic security documents
• Completed project material
• Duplicate files
• Abandoned permissions

Use lifecycle controls to identify inactive sites and ask owners to:

• Renew the site
• Assign a new owner
• Archive it
• Delete it
• Transfer important content

An old site that nobody uses may still be searchable and permissioned.

Inactivity does not make the data harmless.

Review OneDrive During Employee Offboarding

Employee OneDrive accounts frequently contain shared business information.

During offboarding:

• Review sharing links.
• Transfer business files.
• Remove obsolete external access.
• Move long-term records to SharePoint.
• Confirm the new owner.
• Apply required retention.
• Remove temporary delegated access afterward.

A manager receiving full access to a departed employee’s OneDrive can unintentionally inherit personal or unrelated information.

Transfer only business content with a clear ownership decision.

Pilot Copilot With Representative Users

Do not assign Copilot to the entire organisation immediately.

Start with a pilot group including:

• IT
• Security
• Finance
• HR
• Legal
• Operations
• Ordinary knowledge workers
• Site owners

Ask pilot users to report:

• Unexpected documents appearing in results
• Sensitive information they did not expect to find
• Outdated answers
• Incorrect document sources
• Content from completed projects
• Information from unfamiliar sites

Investigate every surprising result as a potential governance signal.

Copilot can effectively become a permission-audit assistant: when it surfaces unexpected information, it may reveal access that already needed correction.

Audit Copilot Activity

Microsoft 365 Copilot interactions may be subject to Microsoft Purview auditing, retention and compliance controls, depending on licensing and configuration.

Audit and compliance planning should address:

• User prompts
• Copilot responses
• Referenced data
• Administrative changes
• Agents and connectors
• Sensitive-information interactions
• Investigation procedures

Define who may investigate Copilot usage and under what circumstances.

Do not give broad access to AI interaction records without privacy, legal and HR review.

Be Careful With Agents and Connectors

Microsoft 365 Copilot is increasingly used with agents and connected data sources.

Every agent should have:

• A defined business purpose
• A named owner
• Approved data sources
• Appropriate access controls
• A review date
• Monitoring
• A retirement process

Review:

• SharePoint agents
• Copilot Studio agents
• Microsoft Graph connectors
• Third-party data connectors
• Custom actions
• External systems

A poorly governed agent can make an existing oversharing problem easier to exploit by concentrating access to large amounts of information.

A Practical Pre-Deployment Remediation Plan

Phase 1: Discover

Before assigning Copilot licences, build a reliable picture of your Microsoft 365 data estate.

• Inventory SharePoint sites, OneDrive accounts, Teams workspaces and Microsoft 365 groups.
• Identify sites with unusually large audiences.
• Find sites containing external users or anonymous sharing links.
• Review inactive, ownerless and unlabelled sites.
• Run permission, sharing and sensitivity reports.
• Identify business-critical and highly confidential locations.

Phase 2: Prioritise

Do not attempt to fix every site at once.

Begin with information that could cause the greatest harm if exposed.

Prioritise:

• Human resources and payroll
• Finance and banking information
• Legal matters
• Board and executive documents
• Cybersecurity investigations
• Customer records
• Commercial agreements
• Intellectual property
• Acquisition and restructuring plans

A lightly used payroll site with excessive permissions may be more urgent than a busy company-news site accessible to all employees.

Phase 3: Remediate

For each high-risk location:

• Remove users who no longer require access.
• Replace broad groups with role-based groups.
• Delete obsolete Anyone links.
• Replace anonymous links with Specific people links.
• Remove former project members and contractors.
• Review unique file and folder permissions.
• Move misplaced confidential information.
• Assign active business and technical owners.
• Archive or delete obsolete sites.
• Apply suitable sensitivity labels.

Every remediation action should have an owner, a reason and a review date.

Phase 4: Add Guardrails

After correcting existing access, introduce controls that reduce future oversharing.

These may include:

• Specific people as the default sharing-link type
• View-only access by default
• Expiration periods for external links
• Guest-access reviews
• Restricted Access Control for sensitive sites
• Temporary Restricted Content Discovery
• Microsoft Purview sensitivity labels
• Data Loss Prevention policies
• Site lifecycle and expiration policies
• Regular permission and sharing reports

Guardrails should support legitimate collaboration rather than blocking every external or cross-departmental workflow.

Phase 5: Pilot Microsoft 365 Copilot

Begin with a representative pilot group rather than deploying Copilot to every employee immediately.

Include users from:

• IT
• Security
• Finance
• HR
• Legal
• Operations
• Management
• General knowledge-worker roles

Ask pilot users to report:

• Documents they did not expect Copilot to find
• Information from unfamiliar sites
• Outdated or obsolete content
• Sensitive information appearing in responses
• Content belonging to completed projects
• Results grounded in documents with unclear ownership

Treat every surprising result as a possible permissions or governance issue.

Phase 6: Expand Gradually

Expand Copilot only after high-risk findings from the pilot have been addressed.

Before each rollout stage:

1. Review the target department’s SharePoint and Teams access.
2. Check OneDrive sharing.
3. Confirm sensitive data is labelled appropriately.
4. Review broad security-group memberships.
5. Confirm site owners are active.
6. Resolve serious oversharing findings.
7. Train users on responsible Copilot use.
8. Monitor results after licences are assigned.

Copilot Oversharing Checklist

Permissions

• Review sites accessible to all employees.
• Identify large or poorly maintained groups.
• Remove former project members.
• Review unique file and folder permissions.
• Check private and shared Teams channels.
• Review external users and guests.
• Remove obsolete anonymous links.
• Confirm sensitive sites have restricted membership.

Content

• Identify confidential and regulated information.
• Apply sensitivity labels.
• Move sensitive files into suitable repositories.
• Remove unnecessary duplicates.
• Archive inactive content.
• Confirm each site has a defined business purpose.
• Assign clear data ownership.

Governance

• Assign at least two owners to important sites.
• Schedule regular access reviews.
• Review group memberships.
• Configure sharing-link expiration.
• Establish a site lifecycle process.
• Document exceptions.
• Create an approval process for sensitive external sharing.

Security Controls

• Use SharePoint Data Access Governance reports where available.
• Configure Restricted Access Control for selected sites.
• Use Restricted Content Discovery as a temporary measure.
• Deploy well-tuned DLP policies.
• Review Microsoft Purview audit settings.
• Monitor external sharing.
• Review Copilot agents and connected data sources.

Deployment

• Begin with a controlled pilot.
• Test realistic sensitive-data questions.
• Investigate unexpected results.
• Train employees on secure prompting and data handling.
• Expand licences gradually.
• Continue quarterly permission reviews.

Common Microsoft 365 Copilot Security Mistakes

Assuming Copilot Created the Oversharing

Copilot normally reflects existing Microsoft 365 permissions. The access problem was usually present before Copilot was enabled.

Assigning Licences Before Reviewing SharePoint

Deploying Copilot first may make years of forgotten access immediately easier to exploit.

Reviewing External Sharing but Ignoring Internal Access

A document can be overshared even when no external users can access it. Employees from unrelated departments may still have unnecessary permissions.

Relying Only on Restricted Search

Discovery restrictions can provide temporary protection, but they do not remove the underlying permissions.

Applying Labels Without Correcting Access

Sensitivity labels improve classification and handling, but a labelled file may still be visible to too many people.

Reviewing SharePoint but Ignoring OneDrive

Important company data is frequently stored and shared from individual users’ OneDrive accounts.

Restricting Everything

Excessive restrictions can undermine Copilot’s value and encourage employees to create new, poorly governed storage locations.

Forgetting Agents and Connectors

An agent connected to broad data sources can amplify an existing access problem.

Treating Copilot Readiness as a One-Time Project

Users, permissions, files and business processes continue to change after deployment. Governance must continue as well.

Final Thoughts

Microsoft 365 Copilot can see more than many organisations expect—not because it ignores Microsoft 365 permissions, but because those permissions are often broader than anyone realises.

Before Copilot, employees generally needed to know where a file was stored, which site contained it and what search terms to use. Copilot can remove much of that discovery effort by finding and summarising relevant information through natural-language requests.

That makes existing permission quality far more important.

A forgotten SharePoint membership, old Teams workspace, broad security group or shared OneDrive folder may allow employees to retrieve information they do not genuinely need for their roles.

The solution is not to hide every document or prevent useful collaboration.

It is to establish intentional access:

Every employee should be able to use the information required for their work—and nothing they do not need.

Before deploying Copilot broadly:

• Inventory your Microsoft 365 data estate.
• Identify sites with broad access.
• Review confidential and regulated information.
• Remove outdated permissions and sharing links.
• Assign active site owners.
• Introduce sensitivity labels and DLP.
• Use targeted access controls for high-risk locations.
• Pilot Copilot with representative users.
• Investigate every unexpected result.
• Continue reviewing access after deployment.

Copilot can become a powerful productivity tool, but its answers will only be as well governed as the information and permissions behind them.

Fixing oversharing before deployment protects sensitive information, improves Copilot’s relevance and gives employees greater confidence in the results it produces.

Worried Copilot Will Surface Overshared Microsoft 365 Data?

Hamilton Group can help your organisation prepare SharePoint, OneDrive and Microsoft Teams for a secure Microsoft 365 Copilot deployment.

Our experts can help you:

• Audit SharePoint and OneDrive permissions
• Identify broadly accessible and overshared sites
• Review anonymous links and external guests
• Run Data Access Governance reports
• Remediate inactive and ownerless sites
• Configure Restricted Access Control
• Apply temporary Restricted Content Discovery
• Deploy sensitivity labels and DLP
• Review Copilot agents and connectors
• Build a phased Copilot pilot and rollout plan
• Establish ongoing access reviews and data governance

Visit hgmssp.com, call Hamilton Group on 0330 043 0069, or book a meeting with one of our experts to fix oversharing before Microsoft 365 Copilot makes sensitive information easier to find.