A backup is only a real backup if an attacker can't touch it. Many backups stay permanently connected to the network, and are therefore just as vulnerable to ransomware as the systems they're meant to protect. Immutable storage exists to prevent exactly that.
Last updated: 24 September 2026Immutable storage is storage where data, once written, cannot be changed, encrypted, or deleted for a set period.
Attackers increasingly target backups first, so recovery becomes impossible before they demand ransom. With stolen credentials, an ordinary backup environment can be wiped. With properly configured immutable storage, that doesn't work as long as the retention period is running.
The best-known implementation is Object Lock, also known as WORM (Write Once, Read Many). Data is written once and remains readable only until the retention period expires. There are usually two modes:
Always ask which mode a provider uses, who can change the retention period, and whether admin accounts have extra protection with MFA.
Immutable storage protects data while it stays connected; the protection lies in the lock. An air-gapped backup isolates the copy physically or over the network. For the strongest protection, the two are often combined.
Immutable storage factors into our Security & compliance criterion. In the provider comparison, you can see for each provider whether immutable storage is included by default or is a separate add-on.
No system is completely invulnerable. In compliance mode, data can't be changed or deleted through the normal storage interface during the retention period, not even with admin rights. The risks mostly lie in configuration: too short a retention period, governance mode with weakly secured accounts, or data that was already compromised before the lock was applied.
That varies by provider. Some BaaS services offer it at no extra cost; with others, you pay for the additional storage the retention period requires.