An immutable backup is a copy of data stored with write protection and a retention window, so it cannot be changed, encrypted, or deleted until the policy expires. This makes it different from a normal backup, which may still be reachable by an attacker who has stolen admin credentials or deployed ransomware.
Immutable backups matter because they give defenders a trustworthy recovery point when live systems are damaged or wiped. In a ransomware event, attackers often try to destroy backups first to block restoration and increase pressure to pay. Organizations use immutability in cloud storage, backup appliances, and offline repositories to preserve critical data, verify recovery, and reduce downtime. It is most effective when paired with access controls, separate credentials, and regular restore tests.