Definition
Immutable backup
In one sentence
An immutable backup is a backup copy that cannot be modified, encrypted or deleted for a set retention period, even by an administrator, protecting it against ransomware and malicious insiders.
Immutable Backup Explained
Ransomware groups routinely target backups before encrypting production systems, because working backups mean the victim does not need to pay. If an attacker gains administrator access and the backup system trusts that access, restore points can be deleted in minutes.
Immutability prevents this. Technologies include object storage with locking features, hardened backup repositories with write-once settings, and backup services that enforce retention independently of customer credentials. The key test is simple: if someone with full admin rights to your network tried to delete your backups, could they? If yes, they are not immutable.
Immutability works best combined with other safeguards: separate credentials for the backup system, MFA on backup consoles, alerts when retention policies change, an offline copy where practical and regular restore tests. Many Canadian cyber insurance applications now ask specifically whether backups are immutable or offline. For SMBs, immutable cloud backup is often the most practical way to meet that expectation, including for Microsoft 365 data.
General information for Canadian organizations, not legal advice.