An external hard drive is a storage device that connects outside the main computer case, usually through USB or another removable interface. It provides portable, high-capacity storage for backups, file transfer, and offline archiving. Because it can be unplugged and moved between systems, it is simple to use but also easy to lose, steal, or misuse.
In cyber security, external hard drives matter because they can bypass network-based defenses. Attackers may use them to move malware into an isolated system, copy sensitive data out of a protected environment, or stage files for later theft. Defenders use them for secure offline backups, forensic evidence collection, and air-gapped storage that is not constantly exposed to the internet. The same convenience that makes external storage practical also makes access control, encryption, and device monitoring important.