Any set of applications with more than 400 million users is going to draw a lot of attention from cyberattackers, and Microsoft 365 falls into that category. Sure enough, cybercriminals love to target the popular productivity suite, formerly called and still frequently known as Office 365.
In fact, since it is both a critical data repository and a primary means of authentication in most organizations’ IT operations, Microsoft 365 is the most targeted platform by far. You need to know how to protect and back up Microsoft 365 (Office 365) so you can keep your data safe and systems running.
Cyberattackers continue to ramp up ransomware attacks
Microsoft 365 ransomware protection is critical because cyberattackers, empowered by AI, are constantly ramping up their attacks. The Acronis Cyberthreats Report H2 2025 offers the kind of terrifying numbers we’re likely to continue to see.
In the second half of 2025:
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Email-based attacks per organization rose 16% year over year.
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Ransomware attacks increased 50% compared to the prior year.
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Phishing accounted for 83% of all email threats in H2 2025.
8 best practices for Microsoft 365 ransomware protection
Security teams can significantly reduce risk by applying proven best practices. Cybersecurity experts at Acronis recommend that admins adopt these best practices to make Microsoft 365 as safe and resilient as possible.
1. Treat identity as the primary Microsoft 365 attack surface
Most Microsoft 365 ransomware incidents start with identity abuse, not malware. Phishing remains the top initial access vector, particularly for managed service providers (MSPs) and cloud-first organizations. Microsoft 365 admins need to respond by strictly enforcing multifactor authentication (MFA) for all users, including admins and service accounts—even if they don’t like it. Disable legacy authentication protocols wherever possible and monitor sign-ins for bizarre travel patterns, risky locations and anomalous behavior. Review conditional access policies quarterly to ensure they still reflect how users actually work. Or better yet, automate policy management and remediation entirely.
2. Use third-party email security to lock down Microsoft Outlook beyond default settings
For starters, it’s essential to add third-party email security solutions, such as the one Acronis provides, to your existing Office 365 setup for an extra layer of protection. Beyond that, Exchange Online Protection catches a large volume of broadly targeted spam, but targeted phishing continues to slip through. Admins should configure advanced phishing protection, impersonation safeguards and safe links policies. Pay close attention to mailbox rules and forwarding settings, which attackers often abuse to maintain persistence and quietly exfiltrate data. Regularly audit those configurations instead of assuming defaults are sufficient.
3. Reduce access points for attackers by controlling Microsoft 365 privileges
Once attackers gain access, collaboration tools become a multiplier for attacks. Admins can slow internal spread and reduce the amount of data available for extortion when they limit who can create groups in Teams, add external users and share files publicly. Apply least-privilege access to SharePoint and OneDrive and review external sharing reports frequently.
4. Patch Microsoft 365 aggressively and close cloud blind spots
Unpatched vulnerabilities remain a major factor in large-scale incidents. Microsoft manages the underlying Microsoft 365 infrastructure, but you have to protect your own data. Organizations should maintain a consistent patching and configuration baseline for devices, browsers and identity integrations that connect to Microsoft 365. For this practice, a third-party patching tool is a necessity for IT teams.
5. Detect ransomware behavior in Microsoft 365, not just malware
Modern ransomware in Microsoft 365 often looks like normal user activity at first. Attackers enumerate mailboxes, download files and prepare for double extortion. Use behavioral detection capable of identifying mass file changes, anomalous downloads and unexpected administrative actions. AI-driven analysis is increasingly important here, especially as attackers themselves use AI to automate reconnaissance and negotiations.
6. Back up Microsoft 365 with recovery in mind
Not all Microsoft 365 backup options are particularly effective. For example, Native retention policies and recycle bins provide limited protection; they are not designed for ransomware‑driven deletion or corruption scenarios. If an attacker deletes data after the retention window or corrupts files gradually, native tools won’t help much. Independent, immutable backups of Exchange, OneDrive, SharePoint and Teams are critical. They allow point-in-time recovery without relying on compromised credentials or production tenants. Again, a third-party solution offers the best option for Microsoft 365 cloud backup for business.
7. Test Microsoft 365 recovery procedures under outage‑level conditions, not only as an audit requirement
Many organizations discover their recovery gaps during an incident when it’s too late. Admins need to regularly test mailbox, file and Teams‑data restoration. Measure recovery time objectives and make sure they align with business impact, not just with compliance checklists.
8. Simplify security operations across Microsoft 365 to reduce IT fatigue
Managing separate tools across identity, email, endpoints and backup increases alert fatigue and slows response time. Consolidated third-party platforms with integrated security, backup and automation reduce complexity and improve visibility across Office 365. For IT teams, many of which are chronically stretched thin, fewer consoles and correlated alerts can make the difference between stopping an attack early and preserving data or responding after attackers have already exfiltrated critical information.
9. Establish zero trust and separation of administrator roles in Microsoft 365
Keep accounts that manage Microsoft 365 security and other functions of the suite separate. An attacker who gets into a single account with both security and general management privileges can do far more damage than one who gets into an account with a single privilege. When you spread responsibility by splitting account types, you limit the damage an attacker can do.
10. Implement Microsoft 365 email archiving
Think ahead about what you’d need in the event of a ransomware attack. Email archiving is the only 100% accurate account of all communications, both incoming and outgoing, via email. Attackers with backup knowledge can send and delete emails that aren’t backed up. Archiving is also critical after the fact for evidence and to supply information to law enforcement or regulators.
11. Give your users security awareness training
Users who lack security awareness significantly increase organizational risk. Reduce the risk of attacks by training users to spot and report them.
Resilience is the new baseline in Microsoft 365 ransomware protection
Protecting your organization against ransomware is about mastering Microsoft 365 cloud backup for business and, as a result, being ready to respond when attackers target credentials and attack at scale. Acronis enables IT teams to combine strong identity controls, visibility across collaboration tools and reliable recovery capabilities. Teams that put those capabilities into place will be better positioned to withstand modern ransomware and data loss without prolonged disruption.
