What are immutable backups?

Immutable backups cannot be changed once written. They rely on WORM (Write-Once-Read-Many) technology, a data storage method in which data is written to storage exactly once and can be read as many times as needed, but it can never be modified or overwritten.

From cyber resilience to regulatory requirements, immutable backups play an important role across industries, particularly in data security and disaster recovery use cases that deal with sensitive data.

For instance, legal records must be tamper-evident: any attempt to alter them needs to be detectable after the fact. Immutable backups satisfy this by preserving data exactly as written and maintaining a chain of custody that process records remain in their original state. The same property is increasingly valuable for AI workloads, which generate large volumes of data needing that same guarantee of integrity.

According to a 2026 Market Reports World report, immutable backups are used in 41% of critical infrastructure facilities. The same report found that 66% of US organizations experienced ransomware attempts on their backup repositories, making ransomware protection one of the primary drivers behind immutable backup adoption.¹

Traditional backups were once the go-to defense against ransomware. Ransomware groups such as LockBit, Qilin and Akira have changed that. Such groups now use artificial intelligence (AI)-driven tools and more sophisticated methods such as ransomware as a service (RaaS) to accelerate attacks and routinely target and infect backup systems before encrypting production data.

According to a 2025 global report from DeepStrike, cyberattacks rose 47%, with cybercriminals utilizing AI across the attack surface.² In another study from Sophos, researchers found that attacks stemming from an unpatched vulnerability led to backup compromise 75% of the time.³ Without a protected immutable backup solution, cyber recovery becomes costly and uncertain.

Immutable data backups deal with these cyberthreats directly. Attackers cannot encrypt, delete or alter them, even with administrative access. This feature provides organizations with a clean, verified copy of data.

Beyond ransomware, immutable backups protect clean recovery points from accidental deletion, corruption and deliberate insider threats. Once a backup is locked, it can’t be altered or deleted by anyone—even someone with full administrative credentials—until the retention period expires

As data volumes grow and organizations increasingly rely on that data for decision-making, data integrity becomes more critical than ever. Healthcare, finance and education organizations alike rely on immutable backups to meet rigid compliance and retention mandates, from HIPPA’s recordkeeping mandates in healthcare, to financial-sector rules like the Digital Operational Resilience Act (DORA) and SEC17a-4, to FERPA’s standards for student records.

While sometimes used interchangeably, immutable backups and immutable snapshots serve different purposes. Immutable backups are self-contained copies of data kept in a dedicated backup system, separate from production.

In contrast, immutable snapshots are read-only, point-in-time copies of data that cannot be altered, modified or deleted by unauthorized users or administrators once created. Unlike backups, snapshots typically reside on the same storage system as the production data they capture, which is what makes them efficient enough to take frequently.

Snapshots are taken more often than backups, providing more granular recovery points and reducing the risk of critical data loss. However, that proximity to production also means that an attack on the storage system itself can destroy them, which is why ransomware often targets snapshots before encrypting underlying files.

When combined, immutable backups and snapshots give organizations layered data protection. Backups provide self-contained restoration points while snapshots provide rapid point-in-time recovery.

Immutable backup systems work across all storage types, including block, file and object storage. They also support a range of deployment models, from on-premises to cloud to hybrid cloud architectures.

Learn more about cloud storage and immutable backup strategies. 

Here is a look at the key concepts and components:

- WORM technology
- Retention locks
- Partitioning
- Air gapping
- Continuous data protection (CDP)
- Encryption and access controls
- AI threat detection

Write-Once-Read-Many (WORM) technology enforces immutability at the hardware or software level—from physical WORM tape to cloud implementations such as IBM Cloud Object Storage, AWS S3 Object Lock. Once written, data cannot be altered or deleted. Without WORM, backups remain vulnerable to the same encryption and deletion attacks that target production data.

Retention locks provide safeguards at the storage level. IT administrators create a retention policy window, and immutable backups stay locked for that entire period. No one can alter or delete them, regardless of their level of access. Retention periods cover known ransomware dwell times, the period an attacker remains hidden inside a network. This function helps ensure that a clean restore point is available.

Backups need to be isolated from production systems. Immutable backups use partitioning to separate components such as the control plane and data plane. Even if attackers get into the primary storage environment, this partitioning prevents them from reaching isolated backup repositories.

Air gap backup physically or logically separates backup data from any network connections—public or corporate—so it cannot be reached by network-based attacks. As an offline copy, it remains intact even if ransomware or another attack compromises production systems, providing a clean recovery point untouched by the cause of the original damage.

Unlike scheduled backups that run at set intervals, continuous data protection (CDP) captures every change to data as it occurs. This capability provides organizations with near-zero recovery point objectives (RPOs), a function that helps minimize data loss even in fast-moving ransomware attacks.

Role-based access and multifactor authentication (MFA) help ensure that only authorized users can manage backup policies and retention settings. Encryption further protects backup data, both in transit and at rest.

Storage systems (for example, IBM FlashSystem, Veeam) use continuous monitoring and machine learning (ML) to analyze data patterns in real time and detect unusual activity, flagging ransomware and malware by distinguishing them from normal behavior. This detection helps pinpoint when an attack began, so organizations can quickly identify which existing snapshot predates the compromise and restore from that unaffected copy.

Organizations depend on backup and disaster recovery technologies to protect data against a wide range of threats, from cyberthreats to system failures. Immutable backups deliver a range of important benefits:

- Data resiliency
- Ransomware protection
- Data integrity
- Regulatory compliance
- Cyber resilience

These strategies can help organizations optimize their approach to immutable backups.

- Plan your deployment
- Choose backup types
- Test regularly
- Integrate with other technologies