# Backup

A copy of data stored separately from the original, used to restore information after loss, corruption, or a ransomware attack.

A **backup[↗](/backup)** is a copy of your important data stored somewhere separate from the original, a different device, drive, or cloud service, so that it can be restored if the original is lost, corrupted, deleted, or encrypted by ransomware[↗](/ransomware). Without a backup, a single hardware failure, theft, or malware[↗](/malware) infection can mean permanently losing photos, documents, or business data.

A widely recommended approach is the 3-2-1 rule: keep at least three copies of your data, on two different types of storage media, with at least one copy stored somewhere physically separate (such as the cloud). Backups only actually protect you if they're tested periodically to confirm they can be restored, an untested backup is really just a hope, not a guarantee.