Microsoft 365 has become the backbone of many businesses, powering email, collaboration, document sharing, and communication. Unfortunately, that also makes Microsoft 365 one of the most common targets for cybercriminals.
A compromised Microsoft 365 account can lead to data theft, financial fraud, ransomware, and business disruption. The good news is that several built-in security features can significantly reduce your risk. Microsoft specifically recommends controls such as multifactor authentication (MFA), blocking legacy authentication, and using Security Defaults or Conditional Access policies to strengthen identity security.
Here are eight security measures every organization should consider implementing.
1. Enable Multi-Factor Authentication (MFA)
If your organization hasn’t enabled MFA yet, this should be your first priority.
MFA requires users to provide a second form of verification beyond a password, such as an approval through the Lastpass Authenticator app.
Microsoft states that MFA helps prevent the overwhelming majority of common identity-based attacks, including password spray and phishing attacks.
Why It Matters
Without MFA:
- Stolen passwords can provide direct account access
- Password reuse becomes extremely dangerous
- Phishing attacks are more likely to succeed
Recommended Approach
- Require MFA for all users
- Require MFA for all administrators
- Use a secure Authenticator App whenever possible like Lastpass
- Avoid relying solely on SMS-based verification
2. Turn On Security Defaults
For organizations without advanced Microsoft Entra licensing, Security Defaults provide a strong baseline level of protection.
Security Defaults automatically:
- Require MFA registration
- Protect administrative accounts
- Block legacy authentication
- Protect privileged activities
- Reduce common identity attack risks
Microsoft notes that Security Defaults are intended to provide baseline identity protection for organizations that need improved security with minimal setup.
3. Block Legacy Authentication
Older authentication protocols often bypass modern security protections and MFA requirements.
Microsoft includes blocking legacy authentication as a core component of Security Defaults because these protocols are commonly targeted by attackers.
Examples of Legacy Authentication
- Older email applications
- Basic authentication protocols
- Outdated Office clients
Benefits
- Reduces password-spray attack success
- Eliminates authentication methods that don’t support MFA
- Improves overall tenant security
4. Implement Conditional Access Policies
For organizations with Microsoft Entra ID P1 (which is included in Microsoft 365 Business Premium licensing) or P2 licensing, Conditional Access provides more granular control than Security Defaults.
Conditional Access allows security policies based on:
- User identity
- Device compliance
- Geographic location
- Sign-in risk
- Application access
Examples
- Require MFA for remote access
- Block sign-ins from high-risk countries
- Restrict access from unmanaged devices
- Require compliant devices for sensitive applications
5. Secure Administrative Accounts
Administrative accounts have elevated permissions and should receive additional protection.
Microsoft specifically enforces stronger protections for privileged activities and administrative accounts within Security Defaults.
Best Practices
- Use separate administrator accounts
- Enable MFA
- Limit the number of Global Administrators
- Review administrative access regularly
- Avoid daily use of administrative accounts
- Have to use some form of Passkey authorization. Good use of Yubikey!
6. Review Sign-In Activity Regularly
Identity attacks often begin with unusual login activity.
Monitoring sign-in logs can help identify:
- Unexpected locations
- Failed login attempts
- Suspicious sign-in patterns
- Unauthorized account usage
What to Watch For
- Logins from unfamiliar countries
- Repeated failed logins
- Unusual after-hours access
- Sign-in attempts from multiple locations
7. Strengthen Email Security
Email remains one of the most common attack vectors.
Attackers frequently use:
- Phishing campaigns
- Business Email Compromise (BEC)
- Invoice fraud
- Credential theft attacks
Recommended Controls
- Microsoft Defender for Office 365
- Anti-phishing policies
- Safe Links
- Safe Attachments
- User security awareness training
Even the best technology can’t prevent every attack, which is why employee training is critical.
8. Protect Data with Backup and Recovery Planning
Many business owners assume Microsoft automatically backs up everything indefinitely.
While Microsoft provides resiliency within the platform, organizations should still evaluate their own recovery requirements and retention needs.
Recommended Strategy
- Backup Exchange Online
- Backup SharePoint Online
- Backup OneDrive for Business
- Backup Microsoft Teams data
- Test recovery procedures regularly
A secure Microsoft 365 environment should include both prevention and recovery measures.
Security Should Be an Ongoing Process
Securing Microsoft 365 is not a one-time project.
As cyber threats continue to evolve, organizations should regularly review:
- MFA coverage
- Administrative access
- Conditional Access policies
- Email security configurations
- Backup strategies
- User awareness training
Organizations that adopt layered identity protections such as MFA, Security Defaults, and Conditional Access significantly improve their security posture against common attacks.
Need Help Securing Microsoft 365?
ComputersDOTCalm helps businesses throughout Southwestern Ontario:
- Deploy Microsoft 365 securely
- Configure MFA and Conditional Access
- Implement Security Defaults
- Reduce phishing risk
- Improve backup and recovery capabilities
- Strengthen overall cybersecurity posture
Book a Free Microsoft 365 Security Assessment
