Why Purview and Defender are powerful – and hard to get right
Welcome to part 3 of our AI Trust Triangle series.
In our first article, we introduced the Trust Triangle as a practical way to think about building trust in an AI-enabled workplace. In the second, we explored identity – not just as login, but as the control layer that determines who can act, in what context, and with what authority.
Today, we turn to the second side of the triangle: data security – and how to control what AI is actually allowed to see and use.
Data security is no longer about locks
AI tools are productivity gamechangers, pulling content and context from across SharePoint, Teams, and email – often instantly.
That capability is undeniably powerful. But it also raises uncomfortable questions.
Employees wonder how much of their work AI can actually access. Leaders ask what counts as sensitive, who can see it, and what happens if something surfaces that shouldn’t.
Those questions don’t arise because AI is breaking through security barriers. They arise because barriers only work when you know what needs protecting, where it lives, how it moves, and who can already access it.
In many environments, that clarity simply isn’t there.
What modern data security actually means
Historically, data security focused on protecting the perimeter.
If data lived inside the network, behind controlled access, it was considered safe. Permissions were set, folders were locked down, and access was assumed to remain stable over time.
That world no longer exists.
Today, data lives everywhere – across Microsoft 365, hybrid environments, endpoints, shared links, collaboration tools, and increasingly, AI-powered workflows.
People access it from everywhere too – corporate devices, personal mobiles, home networks, and increasingly through automation running in the background.
In that environment, security can’t rely on:
- Network perimeters
- Permissions configured years ago
- Manual reviews or guesswork
Modern data security is continuous. It depends on two capabilities working together:
- Visibility – knowing what your data is and where it lives
- Protection and detection – knowing what’s happening to that data in real time
That’s where Microsoft Purview and Microsoft Defender come in.
Purview tells you what the data is. Defender tells you what’s happening to it. They solve different parts of the same problem, and if you’re not using both, you’re either protecting blindly, or watching activity without understanding its impact.
Microsoft Purview: Seeing and classifying the data that matters
Most organisations believe they have a reasonable sense of where their sensitive information lives. Then they turn on Purview and discover far more than expected.
- Personal data in old SharePoint libraries.
- Financial spreadsheets shared more widely than intended.
- HR documents sitting in collaborative folders.
- Confidential project files accessible to broad groups.
By continuously scanning across Microsoft 365 and connected environments to identify sensitive information, Purview can:
- Automatically detect and classify data such as PII, financial records, health information, intellectual property, and other confidential content
- Apply sensitivity labels that travel with the file
- Enforce data loss prevention (DLP) policies based on content and context
- Provide insights into where sensitive data is exposed or overshared
The goal isn’t simply to tag documents. It’s to create a live, accurate map of what matters most so that security decisions can be based on meaningful boundaries, not generic restrictions.
Microsoft Defender: Protecting data in motion
If Purview helps you understand what your data is, Defender helps you understand what’s happening to it – and who (or what) is interacting with it.
Even when data is properly classified and labelled, risk doesn’t disappear. Accounts can be compromised. Files can be downloaded unexpectedly. Sensitive information can move in ways that don’t fit normal patterns.
Microsoft Defender focuses on this behaviour to:
- Detect anomalous sign-ins and compromised accounts
- Alert on unusual file access, large downloads, or potential data exfiltration
- Identify insider risk patterns
- Surface risky automation or AI-driven activity that falls outside established norms
Where Purview builds the map, Defender watches the movement across it. Together, they shift data security from static protection to continuous, informed awareness.
Data Security as a foundation for trustworthy AI
AI is only as trustworthy as the data it can access.
If sensitive information is misclassified, overshared, or poorly understood, AI will operate within those realities. It won’t distinguish between “technically accessible” and “appropriately accessible”. It will simply work with what it’s given.
Together, Microsoft Purview and Microsoft Defender give organisations the visibility and control needed for confident AI adoption.
Not by locking everything down.
Not by slowing innovation.
But by replacing uncertainty with clarity and control.
Before scaling AI, take a long, hard look at your data landscape. Do you know what’s sensitive, where it lives, and who can touch it? If the answer is no, Purview and Defender should be at the top of your agenda – and if you need help making sense of it all, get in touch.