What is Zero Trust security?

Traditional security used a perimeter model: build a strong firewall around the network, trust everything inside. Zero Trust throws that out. The core principle: never trust, always verify. Every access request — even from a user already on the corporate network — is evaluated based on who, what, where, and when.

The three Zero Trust principles

• Verify explicitly — authenticate and authorize every access request using multiple signals (identity, location, device health, sensitivity of resource)
• Use least-privilege access — users get only the permissions they need for the current task, not blanket access
• Assume breach — design controls assuming attackers are already inside; minimize blast radius

What Zero Trust looks like in practice

• Strong identity — MFA on everything, Conditional Access policies (block sign-in from unusual locations, require compliant devices)
• Device health checks — access depends on the device being managed, patched, and compliant with policy
• Microsegmentation — isolate workloads from each other so a compromised endpoint can't roam laterally
• Application-level access — users access specific applications, not the whole network (replace VPN with ZTNA)
• Continuous verification — sessions are re-evaluated based on changing risk signals, not just initial sign-in

Why it matters for SMBs

Zero Trust isn't just for the Fortune 500. Microsoft 365 Business Premium gives SMBs the building blocks: Conditional Access, MFA enforcement, Intune device management, Defender for Endpoint. The Tennessee SMB that implements these properly is dramatically harder to compromise than the one running a firewall and hoping for the best.