Air gap

A security measure where a computer, network or backup is physically isolated from the internet and other networks so that remote attackers cannot reach it.

An air-gapped system has no wired or wireless connection to other networks. Data moves in or out only through deliberate, controlled steps, such as connecting a removable drive. True air gaps are common in industrial control systems, some oil and gas operations and highly sensitive environments.

For most small businesses, a full air gap for everyday systems is not practical. The idea is still very useful for backups. Ransomware groups routinely search for and encrypt or delete backups they can reach over the network. A backup copy that is disconnected, or stored in a way that cannot be changed, gives you a reliable way to recover if everything else is compromised.

Practical tip: keep at least one backup copy that is offline or immutable. That could be a rotated external drive stored securely offsite, or a cloud backup service with immutability features. Remember that an air gap is only as good as the process around it, so a drive left plugged in all the time is no longer air-gapped.