Guidance for Microsoft Defender for Business (MDB) — the SMB-segment endpoint security product (≤300 employees), bundled with Microsoft 365 Business Premium and available as a standalone SKU. Covers what's included vs MDE Plan 1/2 (next-gen AV, EDR with simplified configuration, ASR, automated investigation and response, vulnerability management, web content filtering, attack surface reduction, mobile threat defense add-on), wizard-driven onboarding, server add-on for SMB servers, the simplified portal experience vs full Defender XDR, transition path to MDE P2 / E5 as the org grows, and integration with Microsoft 365 Lighthouse for MSP delivery. WHEN: Defender for Business, MDB, SMB endpoint security, M365 Business Premium security, MDB server add-on, simplified EDR small business, MSP Defender for Business, M365 Lighthouse Defender, SMB upgrade to MDE Plan 2. DO NOT USE for enterprise EDR (use defender-for-endpoint), Defender XDR cross-product investigation (use defender-xdr), or Defender for Servers / Cloud
インストール
Codex または Claude でインストール この Prompt をコピーして Codex、Claude、または他のアシスタントに貼り付けると、Skill ページを確認してインストールできます。
Guidance for Microsoft Defender for Business (MDB) — the SMB-segment endpoint security product (≤300 employees), bundled with Microsoft 365 Business Premium and available as a standalone SKU. Covers what's included vs MDE Plan 1/2 (next-gen AV, EDR with simplified configuration, ASR, automated investigation and response, vulnerability management, web content filtering, attack surface reduction, mobile threat defense add-on), wizard-driven onboarding, server add-on for SMB servers, the simplified portal experience vs full Defender XDR, transition path to MDE P2 / E5 as the org grows, and integration with Microsoft 365 Lighthouse for MSP delivery. WHEN: Defender for Business, MDB, SMB endpoint security, M365 Business Premium security, MDB server add-on, simplified EDR small business, MSP Defender for Business, M365 Lighthouse Defender, SMB upgrade to MDE Plan 2. DO NOT USE for enterprise EDR (use defender-for-endpoint), Defender XDR cross-product investigation (use defender-xdr), or Defender for Servers / Cloud (use defender-for-servers).
license
MIT
metadata
{"author":"Microsoft","version":"0.1.0"}
Microsoft Defender for Business
Defender for Business (MDB) is endpoint security packaged for the small-and-medium-
business (SMB) segment — up to 300 employees. It includes most of MDE Plan 2's protective
power (next-gen AV, EDR, ASR, automated investigation, vulnerability management) with a
simplified, wizard-driven configuration so a small IT team or an MSP can deploy and
operate it without a dedicated SOC.
It's bundled with Microsoft 365 Business Premium and available as a standalone SKU.
For MSPs, it's delivered through Microsoft 365 Lighthouse for multi-tenant management.
When to use
You're an SMB up to ~300 employees, or an MSP delivering security to SMB customers, and
you need real endpoint protection without an enterprise SOC budget.
Do not use this skill for enterprise EDR (defender-for-endpoint), Defender XDR
cross-product investigation (defender-xdr), or Azure server protection
(defender-for-servers).
What's in MDB
Capability
MDB
MDE P1
MDE P2
Next-gen AV
✅
✅
✅
Attack surface reduction
✅
✅
✅
Web content filtering
✅
✅
✅
EDR
✅ (simplified)
—
✅
Automated investigation & remediation (AIR)
✅
—
✅
Vulnerability management
✅ (subset)
—
✅
Threat intel & advanced hunting (Defender XDR)
Limited
—
✅
Mobile threat defense (iOS/Android)
Add-on / via Intune
—
Yes
Server protection
MDB Servers add-on (≤60 servers)
via DfC
via DfC
Rule of thumb: MDB stops where you need a SOC analyst doing advanced hunting in
raw tables. At ~300 users / multi-site / regulated, plan migration to MDE P2 + E5.
Approach
License path. Most SMBs get MDB via Microsoft 365 Business Premium —
bundled with Entra P1, Intune, and DLP basics. Check seat count: MDB is hard-capped
at 300 users; once you exceed, you must move to enterprise SKUs.
Onboard via the simplified setup wizard in security.microsoft.com → Assets →
Devices. Three default device groups: workstations, mobile, servers (servers via
add-on). Wizard pre-configures sensible defaults for AV, ASR, EDR.
Default policies are usable as shipped, but tune two things:
ASR rules — review the audit-mode hits in the first 14 days; promote rules
to block one at a time.
Web content filtering — turn on the categories that match your use (block
gambling, adult, illegal). Don't be aggressive on day one.
AIR remediation level. Default is Semi (require approval). For workstations,
move to Full once the team has confidence. Servers stay Semi.
Vulnerability management. Surfaces top exposures and pushes patch tasks. Pair
with Intune patch management (where licensed) to actually deploy.
Mobile devices. MDB on iOS and Android is delivered via the Defender app
(Intune-managed deployment, recommended). Provides web protection, network
protection, and app risk detection. Real-time AV on Android.
Servers add-on.MDB Servers protects up to 60 Windows or Linux servers per
tenant — adequate for SMB but not enterprise. Onboard via the same simplified
model. Once you exceed 60 or need DfC posture/JIT/FIM, switch to Defender for
Servers (defender-for-servers).
MSP / multi-tenant delivery. Microsoft 365 Lighthouse aggregates MDB across
customer tenants for an MSP:
Cross-tenant device inventory and threat dashboard.
Baseline policy templates pushed to multiple tenants.
Multi-tenant alert triage.
Pair with delegated admin (GDAP) — never DAP — for secure access.
Transition path to enterprise. Trigger criteria for moving to MDE P2 / E5:
Crossing 300 users.
Regulated industry needing advanced hunting / KQL / 30+ day raw telemetry.
Multi-site SOC operation.
Need for Sentinel integration with rich Defender XDR data.
Migration is a license/configuration change, not a re-deployment — devices stay
onboarded.
Guardrails
300-user cap is enforced. Don't architect MDB into a tenant trending toward
enterprise scale; plan E5 / MDE P2 in advance.
Don't turn ASR rules to block on day one. Same as enterprise — audit, tune,
block.
AIR Full mode is fine for workstations, not servers without approval — server
AIR autoremediation can take down apps.
Mobile MDB needs Intune for proper rollout. Without MDM, you rely on user
self-install; coverage is patchy.
Servers add-on is capped at 60. Past that, MDB Servers isn't sized for you;
transition.
Lighthouse + MDB for MSPs requires GDAP, not the legacy DAP — partner relationship
must be migrated.
Advanced hunting is limited in MDB. If your IR practice depends on KQL across raw
Defender tables, you need MDE P2.
Web content filtering is not a SWG. It's category-based, not full inspection.
For real SWG, look at entra-global-secure-access Internet Access.
Don't dual-onboard MDB and a third-party AV in active mode. Set the third-party
to passive + EDR block mode (same rule as enterprise).
Common anti-patterns
"Stayed on MDB at 350 users" — license violation, missing capabilities.
"All ASR rules block on day one" — Office macro and installer breakage.
"AIR Full on servers" — automatic isolation of an LOB app server during a false
positive.
"Mobile rolled out without Intune" — half the fleet unprotected.
"MSP using DAP for tenant access" — should be GDAP; security and audit issue.
"Treated MDB as a permanent solution despite scaling beyond 300" — find out
during audit that the SKU's capped.
"Skipped vulnerability management because 'we patch on Patch Tuesday'" — vuln
prioritization makes Patch Tuesday actually-prioritized.
"Configured advanced policies via Defender XDR portal expecting MDE P2 features"
— features simply aren't available; UI doesn't always make this obvious.
Example prompts
Onboard a 120-user professional services firm to Defender for Business via M365 Business Premium — wizard, ASR rollout, AIR, vuln management.
Plan migration from MDB to MDE Plan 2 + E5 for an SMB approaching 300 users with multi-site operations.
Deploy MDB to 60 servers via the servers add-on; identify gaps requiring Defender for Servers later.
