Immutable backup

An immutable backup is locked for a fixed period once it’s written. Nobody can edit it, encrypt it or delete it early — not a staff member, not your IT provider, and not a criminal who has stolen an administrator password. The lock is enforced by the storage system itself, often called WORM (write once, read many) storage or object lock.

This matters because modern ransomware gangs go after backups first. They break in, find your backup system, delete or encrypt the backups, and only then encrypt your live data — so you have no choice but to pay. A backup they can see but can’t touch takes that leverage away.

Immutability isn’t magic. You still need to protect the backup console with MFA, monitor for failed jobs, and choose a retention period long enough to cover how long an attacker might sit unnoticed in your network — often 30 days or more. And you have to test restores; an immutable copy of corrupted data is still corrupted.

Example: a medical office’s backup service writes nightly copies to cloud storage with a 30-day lock. When an attacker gets in through a phished password and wipes the on-site backup appliance, the practice still has 30 days of locked copies to restore from. Most cyber insurance applications now ask about this kind of protected backup — see our ransomware protection guide.