Introduction to Excel Security Settings

Introduction

You're keeping sensitive models, payrolls, and reports in Excel and need to stop malware and accidental data loss; the goal here is to secure Excel files and materially reduce the risk of malware and data loss. This brief covers the full operational scope: desktop Excel, macros (VBA), add-ins, and external data connections, so controls map to where most breaches start. The outcome: a set of practical settings you can apply now, a 10-point audit checklist to verify compliance, and clear rollout steps (90-day pilot then FY2025 org-wide deployment) so IT and owners can act quickly - one-liner: lock macros, vet add-ins, block unsafe feeds. What this intro hides: the checklist will defintely include policy, configuration, and monitoring items tailored to your environment.

Key Takeaways

• Secure Excel files (desktop, VBA macros, add-ins, external data) to materially reduce malware and data‑loss risk.
• Default to "Disable all macros with notification"; require digital code signing for approved macros and enforce via Group Policy/Intune.
• Enable Protected View for files from the internet/attachments, limit trusted locations, and prefer read‑only review for untrusted files.
• Block automatic external content and unvetted add‑ins; allow only signed/approved COM and Office add‑ins and use network controls and credential prompts for data feeds.
• Operationalize with a 90‑day pilot, a 10‑point audit checklist, user training, and IT Security ownership for org‑wide rollout (target FY2025).

Threat landscape and risks

Describe common attacks: malicious macros, infected templates, phishing links

You're likely seeing Excel files arrive by email or download before you've had a chance to vet them - that's where most attacks start. Malicious actors hide payloads in macros (VBA), weaponize company templates so every user who opens them runs code, or embed phishing links inside spreadsheets to harvest credentials or deliver malware.

One clean line: Treat any unsolicited spreadsheet as hostile until proven otherwise.

Practical steps you can take right now:

• Block or sandbox attachments at the gateway and scan for macros.
• Configure Excel to disable macros with notification and require digital signing for allowed macros.
• Strip or convert inbound .xlsm/.xltm to read-only previews at the mail server.
• Inspect templates centrally; only publish company-approved templates from a secured repository.
• Train users to hover links, not click; show them how to check Trusted Locations and file properties.

What to watch for: mismatched file names and types, strange autorun macros, and files that request credentials or prompt for external connections - they are red flags. Implement email rules that quarantine Office files with macros and route them for human review; it removes a lot of risk without blocking legitimate work.

Show impact: data exfiltration, credential theft, ransomware vector

If a macro runs, it can phone home, drop a loader, or scrape cells and send them out - that's how Excel becomes a data exfiltration tool. Phishing links in sheets lead to credential theft (single sign-on tokens, admin passwords), and infected workbooks are a common initial access vector for ransomware teams.

One clean line: A single compromised workbook can cascade into a multi-day outage and seven-figure loss.

Concrete loss drivers and mitigation steps:

• Data exfiltration: Sensitive columns (SSNs, bank account numbers) should be labeled and blocked by DLP; use file-level encryption and audit access logs.
• Credential theft: Enforce multi-factor authentication (MFA) and avoid embedding credentials in connection strings; rotate service credentials on compromise.
• Ransomware entry: Isolate endpoints, require device health checks via conditional access, and ensure immutable backups with air-gapped or offline copies.

Here's the quick math: stopping one successful macro execution can avoid downstream costs - containment, remediation, legal notification, and lost productivity - that together are typically measured in the high tens to hundreds of thousands of dollars per incident for mid-sized teams. What this estimate hides: the multiplier effect when backups are encrypted or PII is exposed.

Identify high-risk users: finance, HR, external collaborators

You need to segment controls by role because not all users have the same exposure. Finance and accounting open payment files and bank templates, HR maintains payroll and personal data, and external collaborators often bring third-party risk via shared spreadsheets.

One clean line: Lock down the people who handle money and personal data first.

Role-based actions to implement fast:

• Finance: enforce no-macro policies except for signed, approved macros; require dual approval for files that alter payment data.
• HR: restrict downloads of payroll sheets; enable watermarking, DLP, and require password-protected exports.
• External collaborators: require files to be shared via controlled repositories, disable edit-by-link, and put external accounts into a quarantined permission tier.
• Power users: grant exception access via requests tracked in a ticketing system; revoke after 7-30 days unless justified.

Operational note: run an access report this week for users with edit rights on folders containing PII or financial templates; revoke stale permissions and document owner approvals. If onboarding takes 14+ days, the risk from ad-hoc sharing rises - defintely tighten temporary access policies.

Trust Center overview

Show where: File > Options > Trust Center > Trust Center Settings

You're about to lock down Excel settings so risky files don't run code or leak data. Start where users expect: open Excel, click File, choose Options, then Trust Center, and click Trust Center Settings.

In the Trust Center dialog you get a left-hand menu with each control area. If you need to document the path for a helpdesk ticket, write it exactly as File > Options > Trust Center > Trust Center Settings so technicians can follow the same clicks.

One-liner: Open File, Options, Trust Center, then Trust Center Settings.

List key areas: Macro Settings, Protected View, External Content, Add-ins

The Trust Center groups the safest-to-configure items in four practical areas. Below are each area, the concrete controls you'll see, and recommended settings you can apply right away.

• Macro Settings - Options include enable all, disable all macros with notification, disable all except digitally signed, and disable without notification.
• Protected View - Controls for files from the internet, unsafe locations, and Outlook attachments; opens files in a sandboxed, read-only mode.
• External Content - Controls for data connections, workbook links, and automatic update of PivotTables or queries that pull external data.
• Add-ins - Options for COM add-ins, VSTO add-ins, and Office Store add-ins, plus management of inactive or blocked items.

Recommended out-of-the-box posture: set macros to Disable all macros with notification, keep Protected View enabled

One-liner: Treat macros, external data, and add-ins as high-risk and default to block with clear user prompts.

Explain centralized control and policy enforcement options

If you manage more than a handful of machines, don't rely on users changing Trust Center manually. Centralize via Group Policy (ADMX templates), Microsoft Intune (MDM), or the Office Cloud Policy Service so settings apply consistently and survive profile resets.

• Use Administrative Templates (ADMX/ADML) deployed via Group Policy to set Macro Settings, Protected View, Trusted Locations, and add-in behavior at machine or user scope.
• Use Intune to push the same ADMX-backed policies to hybrid and cloud devices; test policies in a pilot group before wide rollout.
• Use the Office Cloud Policy Service for cloud-first estates; it overlays settings for Microsoft 365 apps where GPO isn't available.
• Enforce code signing: require macros to be signed by trusted publishers and publish trusted certificate thumbprints via Group Policy so only vetted macros run without prompts.
• Control trusted locations centrally; avoid per-user trusted folders. Map any approved network locations via policy and mark them as read-only where possible.
• Deploy add-ins centrally using centralized deployment (for Office add-ins) or via SCCM/Intune for COM/VSTO, and whitelist by publisher or file hash where supported.
• Audit and monitor: enable event logging for Office application security events, collect logs via SIEM, and run periodic reports to detect policy bypass or unsigned macros.

Practical rollout steps: export current GPO settings as baseline, apply strict policy to a pilot group, fix blockers, then apply broadly. If you have an internal CA, publish a code-signing certificate and register its thumbprint in policy so approved macros run for users without turning off protections - this step is simple but defintely high impact.

One-liner: Enforce Trust Center controls from the top down with GPO/Intune and require code signing for any macro exception.

Macro and VBA controls

Set policy: Disable all macros with notification by default

You're keeping users productive but need to stop macros from being the easiest attack path; start by making the default setting safe.

Practical steps for you:

• Open Excel: File > Options > Trust Center > Trust Center Settings > Macro Settings and choose Disable all macros with notification.
• Pilot with a controlled group (finance and IT power users, about 5-10% of users) for 7-14 days to capture false positives and legitimate workflows.
• Communicate the change in advance: explain the notification dialog, how to request approval, and the expected response SLA (example: 48 hours for IT review).
• Create a lightweight exception workflow: ticket + justification + sample file for IT to validate before granting an exception.

One-liner: Disable macros by default and ask users to request exceptions.

What to watch for and considerations:

• Power users will hit the prompt frequently; collect a list of recurring prompts to create permanent, signed exceptions instead of broad allowlists.
• If a critical automated process breaks, capture the file, run static analysis (e.g., VBA code scan), then sign or replace the macro-do not widen global macro settings.
• Expect short-term helpdesk load; staff training and clear request steps lower repeat tickets.

Use digital code signing for approved macros (trusted publishers)

You want approved macros to run without friction and unapproved macros blocked; digital code signing makes that possible.

Step-by-step signing and trust model:

• Issue code signing certificates from an internal PKI (Active Directory Certificate Services) or buy from a commercial code-signing CA; prefer internal CA for internal-only macros.
• Have macro authors sign VBA projects in the VBA editor: Tools > Digital Signature, select the certificate, save the workbook as a macro-enabled file.
• Publish the certificate to users as a Trusted Publisher or install the CA root into Trusted Root Certification Authorities and the signer cert into Trusted Publishers via Group Policy.
• Maintain a certificate inventory and rotate certificates before expiry; set a reminder at least 90 days before expiration.

One-liner: Sign approved macros and distribute the signer certificate to Trusted Publishers.

Best practices and guardrails:

• Require code review before signing; keep a changelog and versioned repository for signed macros.
• Limit signing rights to a small set of developers or an automated signing service; do not let end users self-sign for production use.
• If you must accept third-party signed macros, validate the signer identity and revoke trust if compromise is suspected.

Enforce via Group Policy/Intune for organization-wide consistency

You need the setting applied consistently across domain-joined and remote devices; use Group Policy for on-prem and Intune for cloud-managed devices.

Implementation checklist:

• Download the latest Office ADMX templates from Microsoft and add them to your Group Policy Central Store.
• In Group Policy Management, configure the Office policy named VBA Macro Notification Settings to enforce Disable all macros with notification and enable Block macros from running in Office files from the Internet.
• For Intune, create a Device Configuration profile using Administrative Templates, set the same ADMX-backed settings, or deploy the equivalent registry keys via a PowerShell script assignment.
• Deploy in phases: pilot (5-10% users), ramp (25-50%), full (100%) with monitoring windows between phases.

One-liner: Push the macro policy centrally with ADMX/Intune and roll it out in stages.

Operational notes and fallback plans:

• Log macro-enable events and maintain a ticketed exception register; use event logs or endpoint telemetry to detect bypass attempts.
• For non-domain devices, use Intune or an MDM to push registry keys and certificates; fallback to an automated support script for edge cases.
• Run a 30-day review after full deployment to validate reduced macro incidents and adjust exceptions; IT should own the review and update cadence.

Protected View and file validation

You're opening Excel files from email, downloads, or external partners and want to avoid malware, credential theft, or accidental data loss - this section shows how to use Protected View and file validation to make that safer, with practical steps you can apply now.

Explain Protected View: sandbox for files from internet/attachments

Protected View is Excel's read-only sandbox that opens potentially unsafe files (email attachments, downloads, internet files) without running active content like macros or XLL add-ins.

How it works: Excel isolates the file process, disables editing, blocks macros, and stops external data connections until you explicitly allow editing. That prevents many malware vectors from executing automatically.

Turn it on or check it: File > Options > Trust Center > Trust Center Settings > Protected View - enable the three boxes for files from the internet, Outlook attachments, and files in potentially unsafe locations.

Quick action steps:

• Keep Protected View enabled
• Scan file with antivirus before enabling editing
• Prefer copying content to a new workbook if unsure

One clean line: Open first, edit later.

Configure trusted locations sparingly; prefer read-only review

Trusted Locations bypass Protected View and allow active content to run, so every trusted folder increases risk. Only add locations when you control the source and file access.

Practical rules for Trusted Locations:

• Allow only specific folders
• Avoid network shares unless tightly controlled
• Disable trusting subfolders by default

Steps to add a safe location: File > Options > Trust Center > Trust Center Settings > Trusted Locations > Add new location - document the business justification and owner each time.

Safer alternatives: use Trusted Documents (Excel remembers a file you explicitly trusted) or require macro code signing so you don't rely on folder-level trust.

One clean line: Trust folders rarely, trust code deliberately.

Balance: reduce prompts for power users, keep strict defaults for others

You need a practical balance: strict defaults for most users, targeted relaxations for vetted power users who need frequent editing or automated sheets.

How to implement policy at scale:

• Set strict defaults in the Trust Center
• Use Group Policy or Intune per AD group
• Require macro signing for exceptions

Example rollout: keep Protected View and Disable all macros with notification by default; for a finance power-user group, allow signed macros and specific trusted folders managed by IT. Track exceptions in a ticket and review them quarterly.

Operational tips: document exception owners, require code signing, and run periodic scans of trusted locations. It's defintely safer to centralize exception approvals.

One clean line: Strict by default, narrow exceptions only.

External content, data connections, and add-ins

You're using Excel files that pull data from the web, other workbooks, or third-party add-ins, and that's your primary attack surface right now; lock defaults to safe and only allow exceptions you can audit. Here's the short takeaway: disable automatic external content, allow only signed add-ins, and force credential prompts at the connection layer.

Disable automatic external content (queries, links) by default

Start from the Trust Center (File > Options > Trust Center > Trust Center Settings > External Content) and set workbook links and data connections to either prompt or disable automatic updates. That stops Excel from silently pulling content that can carry macros, exfiltrate data, or trigger web-based exploits.

Concrete steps:

• In External Content, choose Disable automatic update of Workbook Links or Prompt.
• Set Data Connections to Prompt or Disable automatic refresh.
• In Data > Queries & Connections, open each query's Properties and uncheck background refresh and automatic refresh on open.
• Document exceptions: require a business case, owner, and expiry date for any connection allowed to auto-refresh.

What to watch for: Power Query and legacy connections can bypass expected prompts; audit Query folders and shared templates monthly. One-liner: default to no auto-refresh and only grant exceptions with an owner.

Audit and allow only signed COM and Office Add-ins

Inventory every add-in first: File > Options > Add-ins, then Manage COM Add-ins and Manage Office Add-ins to list installed components. Remove anything unused or from unknown publishers. Unsigned COM add-ins are a common persistence vector-treat them like executable code.

Practical controls:

• Require code signing for add-ins and accept only certificates from your CA or trusted publishers.
• Use centralized deployment (for Office Add-ins) and an allowlist to push vetted add-ins to users.
• Use endpoint controls (AppLocker/WDAC) to block unsigned DLLs and COM components from loading in Office processes.
• Keep a change log: publisher, thumbprint, version, deployment date, owner.

Operationalize: set Group Policy or Intune to block unsigned add-ins and require admin approval for new ones; do quarterly revalidation. One-liner: only signed, whitelisted add-ins get production access-everything else gets blocked or sandboxed.

Use network-level controls and credential prompts for data sources

Network controls reduce blast radius. Limit outbound traffic so Excel clients can only reach approved data endpoints (IP allowlists, proxy, DNS filtering). For cloud/SaaS sources, enforce Conditional Access and MFA so stolen credentials won't give silent access to data feeds.

Connection hardening steps:

• Require per-connection authentication prompts; do not save passwords in connection strings or ODBC DSNs.
• Use service accounts with least privilege for scheduled server-side refreshes and log those accounts separately.
• Place DBs behind private endpoints (Azure Private Link, VNet) or IP-restricted firewalls so Excel must use an approved gateway.
• Use a gateway (on-prem or cloud) that enforces TLS, inspects queries, and logs connection attempts centrally.

Example policy: block all direct outbound DB ports from clients, allow only proxy-to-approved-endpoints, and require reauth every 24 hours for sensitive refreshes. One-liner: stop direct client access-force every connection through a controlled, logged path.

Action checklist and rollout owner

You should lock macros, turn on Protected View, and tighten trusted locations now, then audit and enforce those settings org-wide within 30 days. This reduces the highest-risk attack vectors (malicious macros, infected templates, and external-content exploits) quickly.

Quick checklist: concrete settings to apply

Apply these settings first on a test workstation, then push by policy.

• Open Excel: File > Options > Trust Center > Trust Center Settings
• Macro Settings: choose Disable all macros with notification (default safe choice)
• Protected View: enable all three checks (files from internet, unsafe locations, Outlook attachments)
• Trusted Locations: remove network and user-writable paths; allow only specific signed folders
• External Content: disable automatic refresh for data connections and linked workbooks
• Add-ins: allow only signed COM and Office Add-ins; set user install to blocked where possible

One-liner: set macros to disable-with-notification, enable Protected View, and lock trusted locations.

Next steps: audit, enforce, and train

Run a short audit to baseline current exposure, then enforce settings and train users.

• Audit: export Trust Center settings from a sample of workstations (target 50 users or 5% of the estate, whichever is smaller)
• Inventory: list files in existing Trusted Locations and map any business-critical macros or add-ins
• Pilot: deploy policy to a pilot group (50 users) for 7 calendar days, collect breakage reports
• Enforce: apply Group Policy or Intune configuration profiles to set Trust Center defaults and lock down Trusted Locations
• Train: deliver a 45-minute live or recorded session, plus a one-page quick reference and a phishing/macro simulation

Here's the quick math: audit (2 days), pilot (7 days), deploy (7 days), train (7 days) = ~23 days; add buffer to hit 30 days. What this estimate hides: remediation of broken business macros can add extra time.

One-liner: audit first, pilot second, lock by policy, then train users.

Owner and immediate next step

Make IT Security the rollout owner and assign clear operational roles.

• Owner: IT Security - overall program lead
• Desktop/Endpoint team: implement Group Policy/Intune profiles and test deployments
• Helpdesk: prepare runbook and triage playbook for reported macro/add-in breakages
• Application owners: validate and sign any critical macros (code signing) within pilot window
• Compliance: record decisions and exceptions in a central register

Immediate next step (owner action): IT Security to schedule the audit start date and pilot cohort by calendar day 30 from today; assign Desktop team to create the Group Policy/Intune profile within 7 days. defintely confirm the pilot list with business leads.

One-liner: IT Security owns scheduling and must start the audit and pilot within 30 days.