Yes—ransomware can damage files stored in SharePoint Online. It may run on a user’s computer and encrypt, rename, or delete files in a synced library, with those changes then syncing to SharePoint. An attacker using a compromised Microsoft 365 account is a separate route. Neither cloud storage nor recovery features make a tenant immune; reduce the risk with strong identity and access controls, and prepare recovery before an incident.
How do ransomware attacks affect SharePoint?
Microsoft describes a local-sync route: ransomware executes on a connected computer and manipulates files in a mapped SharePoint library or a library connected through OneDrive. The sync client or WebDAV can then carry those changes to the online library. The malware may encrypt files, append an unfamiliar extension, or delete files. In this pattern, the malware runs on the endpoint; SharePoint receives the resulting file changes.
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A different route begins with a compromised user account. An intruder can use that account to access and change resources its permissions allow. Broader permissions can increase the number of sites and files within reach, and accounts with elevated rights can present greater risk. The two routes can overlap, but protecting the sync-connected computer does not by itself secure a stolen account, and securing an account does not by itself stop malware already running on a device.
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What signs call for immediate action?
Microsoft identifies these possible warning signs in a SharePoint library:
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- Many files show the same Modified By timestamp.
- Files will not open or appear corrupted.
- Ransom instructions appear in folders.
- Filenames have changed or have an unfamiliar extension appended.
These signs warrant urgent investigation, but they do not alone establish the cause or extent of an incident. Follow your organization’s incident-response process and involve its IT or security team.
What should an administrator do first?
- Stop further synchronization. Microsoft advises immediately stopping OneDrive sync or disconnecting the mapped drive to the affected SharePoint library. This helps prevent more endpoint changes from propagating while the incident is assessed.
- Notify the response team and contain access. Contact your incident-response or IT administrator. Contain the affected endpoint and any suspected compromised account before reconnecting devices or restoring data.
- Preserve the facts needed for recovery. Record affected site collection URLs and the last known clean modification time, along with relevant incident details. Keep these available when planning a restore.
- Choose a restore point only after containment. Use the applicable SharePoint restore procedure or Microsoft 365 Backup if it is available and appropriate. Do not reconnect sync or treat a restore as a substitute for investigating and containing the endpoint or account.
- Escalate if standard recovery paths are insufficient. Microsoft says SharePoint retains backups for 14 days beyond actual deletion and advises administrators to contact support within that window when normal restore paths fail. This is a post-deletion support window, not a guarantee that every file can be recovered.
How can administrators reduce SharePoint ransomware risk?
Protect accounts, especially high-impact accounts
Require multifactor authentication (MFA), prioritizing administrator and other accounts whose access could affect many sites or users. Where licensing and configuration allow, use Conditional Access and identity-risk controls. Microsoft recommends passwordless authentication for Microsoft Entra ID accounts and identifies FIDO2 security keys, Windows Hello for Business, and certificate-based authentication as phishing-resistant approaches. Apply stronger sign-in requirements to sensitive access where feasible, while ensuring users and administrators have supported methods and a recovery process.
Restrict permissions and limit the blast radius
Inventory sensitive sites and data, grant only the access and actions people need, and review who can edit or delete important content. Avoid broad edit or delete permissions when narrower access will work. Monitor for overly broad permissions and audit access to sensitive locations. These controls limit what a compromised account can reach; they do not prevent every authorized user or infected device from changing files within its allowed scope.
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Maintain security baselines and device protections, and configure attack detection and response. Use available phishing and malware controls to reduce the chance that a user or device becomes the entry point. Anti-phishing controls may help detect malicious messages associated with ransomware campaigns; they cannot decrypt files that have already been encrypted.
Make recovery settings and procedures usable
Check versioning and retention settings for important libraries, understand the scope and limits of recycle-bin and restore features, and document who is authorized to perform recovery. Exercise the process against the organization’s needs so that staff know how to select a clean point and restore without prematurely reconnecting affected devices. Microsoft notes that reducing version history can reduce the effectiveness of Files Restore.
Assess whether extended backup is needed
Microsoft recommends evaluating Microsoft 365 Backup or a recognized partner solution built on Microsoft 365 Backup Storage when an organization needs longer protection or fast bulk recovery. Compare restore scope, age and frequency of available restore points, speed, retention, licensing, and operational requirements. Check whether a partner solution uses Microsoft 365 Backup Storage rather than assuming that all third-party copy products offer equivalent recovery performance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Which SharePoint recovery option fits the incident?
Recovery features have different scopes and dependencies. Microsoft describes the following settings and capabilities; they are not independent guarantees of what a particular tenant can recover. Confirm current service documentation and tenant configuration before relying on them.
| Recovery option | What it can help recover | Microsoft-documented window or setting | Important qualification |
|---|---|---|---|
| Version history | Earlier versions of an individual file, useful for undoing malicious or accidental changes. | Microsoft’s version-history documentation does not establish one universal retention period in the cited material. | Availability depends on version settings. Restoring a version makes it the new current version; version history is not prevention or a complete incident-response plan. |
| SharePoint recycle bin | Deleted items, subject to recycle-bin behavior. | Microsoft documents 93 days of retention from deletion from the original location, across recycle-bin stages (2025). | Applies to deletion recovery; it is not a general restore of every overwritten or encrypted file. |
| Files Restore | A SharePoint document library restored to a point in time. | Microsoft documents restoration to a point within the prior 30 days (2025). | Version-history settings affect how useful Files Restore can be. |
| Microsoft 365 Backup | Full SharePoint site restores, or more granular SharePoint and OneDrive file and folder restores. | For full SharePoint site restores, Microsoft documents 10-minute restore points for the most recent 0–14 days and weekly points for 15–365 days. For granular file and folder restores, points are roughly daily for 0–14 days and weekly for 15–365 days. | Intervals are workload-specific and Microsoft notes rare exceptions. Check current service documentation, tenant availability, and configuration. |
| Microsoft support after deletion | An escalation path when normal restore options fail after actual deletion. | Microsoft’s ransomware guidance describes 14 days of additional post-deletion recovery support. | Contact support within that period if normal paths fail; it is not a substitute for configured backups or a promise of recovery. |
When selecting a recovery path or evaluating an additional backup service, match the option to the incident: file-level recovery may be enough for a small number of changed documents, while widespread damage may call for site-level or bulk recovery. Also account for how old a clean point can be, restore-point frequency and potential data loss, restore speed, retention, versioning dependencies, licensing, and who will operate the restore.
Microsoft’s documentation characterizes version history as part of built-in data protection in SharePoint and OneDrive. That protection can make earlier file states available, but recovery still depends on the incident, configured settings, and whether a clean point remains available.
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