# Immutable Backups: Protection Against Ransomware
Ransomware changed backup strategy. Attackers learned that encrypting production data is insufficient if backups enable recovery. Modern ransomware targets backup systems explicitly. Deleting or encrypting backups before deploying ransomware maximises leverage.
Immutable backups counter this threat. Once written, backup data cannot be modified or deleted for specified retention periods. Even administrators with full access cannot alter immutable backups. Ransomware cannot encrypt what it cannot modify.
## Immutability Concepts
Understanding immutability implementation clarifies protection.
**Write Once Read Many (WORM)** prevents modification after writing. Data remains readable. No deletion or overwriting possible. Common in compliance scenarios.
**Retention lock** prevents deletion for specified duration. Data can be read. Cannot be deleted until retention expires. Some implementations allow extending but not shortening retention.
**Legal hold** preserves data indefinitely. Used for litigation or investigation. Overrides normal retention policies. Data preserved until hold released.
## Implementation Options
Multiple technologies provide immutability.
**Object storage with locking** leverages cloud capabilities. S3 Object Lock and Azure immutable blob storage. Governance and compliance modes offer different protection levels.
**Purpose-built backup appliances** include immutability features. Vendors offer WORM storage capabilities. Integrated with backup software for seamless protection.
**Air-gapped copies** provide physical separation. Offline tapes or disconnected disks. Cannot be reached by network-based attacks. Manual processes required.
**Linux hardened repositories** use operating system features. Immutable file attributes. Restricted access even for root. Veeam popularised this approach.
## Implementation Considerations
Immutable backup deployment requires planning.
**Retention policies** balance protection and cost. Longer retention provides more recovery options. Storage costs increase with retention. Align with business requirements.
**Access controls** limit administrative exposure. Separation of duties for backup administration. Multi-person authorisation for critical changes. Protect the protection.
**Testing** validates recovery capability. Immutable backups only help if recovery works. Regular restoration testing required. Document and practice procedures.
**Gaps in coverage** must be identified. Not all data may be protected. Legacy systems may not support immutability. Risk assessment identifies gaps.
If your organisation needs help implementing ransomware-resistant backup architecture, contact us through our contact page.
## Immutability Done Properly
Immutability must be enforced *outside* the compromised environment. If an attacker can delete the backup policy, it is not immutable.
Look for:
- write-once storage,
- separate admin identities,
- and retention locks.
## Operational Checklist
- test restores,
- monitor backup job failures,
- and ensure backup credentials cannot access production systems beyond what is needed.
The goal is a clean restore path even after total domain compromise.