The short answer is reassuring and alarming at the same time. Copilot doesn’t get any special access to your files. Microsoft says it plainly: Copilot “only surfaces organizational data to which individual users have at least view permissions” (Microsoft Learn). If Sarah in reception can’t open the salary spreadsheet today, Copilot won’t show it to her tomorrow.
The alarming part is the word “can”. Most firms have never looked at what each person can open. They know what people do open, which is a much smaller list. Copilot closes that gap. A search box that used to need the exact file name now answers questions like “what do the partners earn?”, and it answers from anything the person asking has permission to read.
Where the surprises usually are
After enough Microsoft 365 setups, the same five places come up again and again. None of them is anyone’s fault. They’re what ten years of getting work done leaves behind.
1. Links shared with everyone in the firm. Someone needed to send a file quickly in 2019, picked “People in your organization”, and moved on. That link still works, for every account, including ones created last month. Microsoft documents the link types and what each one opens (Microsoft Learn).
2. Sites opened to “Everyone except external users”. This is the setting that turns a department’s site into the whole firm’s site. It’s often added to fix one access problem and never removed.
3. Folders that stopped following their site’s rules. When a folder is shared on its own, it can end up with different permissions from the site around it. The site looks locked down. One folder inside it isn’t.
4. Accounts nobody switched off. Former staff, a temp from two summers ago, a shared mailbox someone could still sign in to. An account that still works can still read everything it could read on its last day. Microsoft’s guide to cutting off access when someone leaves is a useful checklist even if you never use Copilot (Microsoft Learn).
5. Apps that were given access to mailboxes and files. A note-taker, a scheduling tool, a PDF converter. Each one asked for permission once, someone clicked “Accept”, and some of them can read far more than they need. Whether staff can approve these on their own is a setting you control (Microsoft Learn).
How to find them before you switch Copilot on
You don’t have to read every folder. Microsoft has built most of the tools you need:
- The data access governance reports in the SharePoint admin centre list the sites with the broadest access, including those shared with “Everyone except external users”, and the sharing links in use (Microsoft Learn). They need the right licence; the page lists which.
- Microsoft’s oversharing blueprint is a step-by-step plan for exactly this job, written for firms deploying Copilot (Microsoft Learn). It’s long, but it’s the official order of work.
- Restricted Content Discovery keeps chosen sites out of Copilot’s answers and organisation-wide search while you review them (Microsoft Learn). It’s a pause button, not a fix. The permissions underneath stay as they are.
The honest catch is time. The reports tell you where to look. Someone still has to open each site, decide what it should be, and change it without breaking the way people work. In a 30-person firm that’s usually a few days of careful work, not a few minutes [Estimate].
What to fix first
If you only have an afternoon, do it in this order:
- Switch off the accounts of people who’ve left. It’s the quickest win, and it closes the oldest doors.
- Find the five sites with the broadest access and ask whether everyone in the firm really needs them. Finance, HR and partner folders are the usual answers to “no”.
- Replace “everyone” links on anything sensitive with links to named people.
- Check which apps can read mailboxes and remove the ones nobody recognises.
Then, and only then, give Copilot to a small group first. Nothing goes to the whole firm on day one.
What this isn’t
This isn’t a reason to avoid Copilot. When the permissions are tidy, it’s genuinely useful: drafting the reply, finding the right contract, summarising the meeting you missed. The work above is what makes it safe to enjoy. It also tends to fix problems that had nothing to do with AI, which is a nice side effect.
Nobody’s in trouble, either. Every firm I’ve seen has some of this. The ones that do well are the ones that look before they switch it on.
If you’d rather I looked
Everything above is on the free AI Guardrails checklist, item by item, with where to find each setting. If you’d rather I did it, the AI Exposure Check is where I start: two weeks, read-only, and you get in writing what Copilot could see in your Microsoft 365 today, who actually needs a seat, and the three things to fix first.
Sources: Microsoft Learn, as linked above, checked 8 November 2026. Microsoft renames features often; if a link has moved, the page title will still find it.