Microsoft 365 Security: How to Protect Your Data After Migration
Microsoft 365 is secure by design, but businesses must take extra steps to protect against phishing, malware, insider threats, and data breaches. Without the right security configurations, emails, files, and sensitive business data could be at risk.
This guide will walk you through Microsoft 365 security best practices to ensure your business emails, files, and user accounts remain protected after migration.
Why Microsoft 365 Security Matters
Ransomware & Phishing Attacks on the Rise – 94% of cyberattacks start with a phishing email.
Weak Passwords Cause 81% of Data Breaches – Without Multi-Factor Authentication (MFA), your business is vulnerable.
Insider Threats & Data Leaks – 60% of security incidents come from employees accidentally or intentionally leaking data.
💡 A strong Microsoft 365 security setup is essential to protect your emails, files, and business operations from cyber threats.
Microsoft 365 Security Best Practices: Step-by-Step Guide
Enable Multi-Factor Authentication (MFA) for All Users
Why? Passwords alone are not enough—MFA prevents 99.9% of account breaches.
How? Requires users to verify logins using Microsoft Authenticator, SMS, or security keys.
How to Enable MFA in Microsoft 365:
Go to Microsoft 365 Admin Center → Active Users
Select users → Click Enable Multi-Factor Authentication
Require MFA for all users, especially admins
Encourage employees to use Microsoft Authenticator instead of SMS (more secure)
💡 For added protection, enable Conditional Access MFA, which prompts MFA only on high-risk logins.
Set Up Conditional Access Policies & Endpoint Security
Why? Blocks unauthorized logins & secures remote access.
How? Restricts Microsoft 365 access based on location, device, or user risk level.
How to Configure Conditional Access in Azure AD:
Open Microsoft Entra (formerly Azure AD) Admin Center
Navigate to Security > Conditional Access
Create a new policy:
Require MFA for logins from new locations
Block access from risky devices (e.g., unregistered, jailbroken phones)
Restrict admin logins to corporate devices only
Apply policies to all users, especially high-risk accounts
💡 Use Microsoft Defender for Endpoint to secure employee devices against malware and data theft.
Protect Business Emails from Phishing & Malware
Why? 94% of cyberattacks begin with malicious emails (phishing, malware, ransomware).
How? Enable Microsoft Defender for Office 365 to block dangerous emails before they reach inboxes.
How to Enable Anti-Phishing Protection:
Go to Microsoft 365 Defender Admin Center
Navigate to Policies & Rules > Threat Policies
Enable Safe Links & Safe Attachments (Blocks malicious links & attachments in emails)
Configure Anti-Phishing Policies: Warn users when emails look like spoofed internal emails; Quarantine emails flagged as high-risk phishing attempts
Use Microsoft Defender for Office 365 Plan 2 for real-time phishing detection
💡 Enable automatic impersonation detection to stop email spoofing attempts.
Prevent Data Loss with Microsoft 365 DLP Policies
Why? Prevents employees from accidentally or intentionally sharing sensitive business data.
How? Blocks unauthorized sharing of credit card numbers, customer data, and confidential files.
How to Set Up Data Loss Prevention (DLP) in Microsoft 365:
Open Microsoft 365 Compliance Center
Navigate to Data Loss Prevention > Create Policy
Choose a template (e.g., Financial Data, GDPR, HIPAA)
Apply policies to: Emails (Exchange Online); Files (OneDrive, SharePoint); Microsoft Teams messages
Set up alerts & automatic actions: Block external sharing of sensitive data; Warn users before sending protected files
💡 Enable Microsoft Purview (formerly Information Protection) to classify & encrypt business documents.
Secure OneDrive & SharePoint Files
Why? Prevents data leaks, accidental deletions, and insider threats.
How? Set strict file-sharing rules, version history, and access controls.
1. How to Secure OneDrive & SharePoint Data
Restrict External Sharing:
Go to Microsoft 365 Admin Center > OneDrive Settings
Disable anonymous file links
Allow sharing only with approved external partners
Enable Version History & Auto Backup:
Allows recovery of accidentally deleted or overwritten files
2. Apply Sensitivity Labels to Important Documents:
Labels like “Confidential” or “Internal Use Only” control how files can be shared.
💡 Use Microsoft Defender for Cloud Apps to detect suspicious file access attempts.
Advanced Security Features for Enterprises
For companies with strict security & compliance requirements, Microsoft 365 offers enterprise-grade protection:
Microsoft Defender for Endpoint – Blocks malware & ransomware on work devices.
Microsoft Sentinel (SIEM) – AI-powered security analytics for detecting cyber threats.
Privileged Identity Management (PIM) – Protects admin accounts from privilege abuse.
Insider Risk Management – Detects risky user activity (e.g., mass data downloads before leaving the company).
💡 Upgrade to Microsoft 365 E5 for full threat detection & automated incident response.
Common Microsoft 365 Security Mistakes & How to Fix Them
🚨 Mistake #1: Not Enforcing Multi-Factor Authentication (MFA)
✅ Fix: Require MFA for all accounts, not just admins.
🚨 Mistake #2: Allowing Unrestricted File Sharing
✅ Fix: Restrict OneDrive & SharePoint external sharing settings.
🚨 Mistake #3: No Security Monitoring in Place
✅ Fix: Enable Microsoft Defender threat reports & alerts.
🚨 Mistake #4: Weak Password Policies
✅ Fix: Enforce strong password policies & use passphrases instead of simple passwords.
🚨 Mistake #5: Ignoring Insider Threats
✅ Fix: Set up Data Loss Prevention (DLP) & Insider Risk Management policies.
Final Thoughts: How to Keep Your Microsoft 365 Business Secure
Moving to Microsoft 365 improves productivity—but without the right security settings, your business could be at risk.
Enable Multi-Factor Authentication (MFA) to block unauthorized access
Use Conditional Access Policies to protect against risky logins
Set up Microsoft Defender to stop phishing & ransomware
Apply Data Loss Prevention (DLP) rules to prevent data breaches
Secure OneDrive & SharePoint files with sharing restrictions
Need help securing your Microsoft 365 environment? Advance IT specializes in Microsoft 365 security audits & compliance solutions. Contact us today to ensure your business data stays protected!
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