Backups

CISA's 3-2-1 rule asks for three copies of every important file, on two kinds of storage, with one copy kept somewhere other than your home or office.

A rule first written down for photographers

That 2012 paper, Data Backup Options, credits Krogh's book on digital asset management and sets the rule out in three parts. Keep 3 copies of any important file: the original and two backups. Keep them on 2 different types of media, so one kind of failure cannot take out both; for example the computer's own disk and an external drive, or an external drive and online storage. Store 1 copy off site, away from your home or business, so a fire, flood or burglary does not take every copy at once.

The many ways a file disappears

Files are lost in many ways: a laptop is dropped or stolen, a drive wears out, a coffee goes over the keyboard, a file is deleted by mistake, or ransomware scrambles everything. Ransomware is malware that encrypts the files on a device so that they are unusable, and its operators then demand payment for the key. More and more they also copy the data first and threaten to publish it. A good backup turns all of these from a disaster into an inconvenience. CISA's StopRansomware guidance puts it simply: backing up is your best bet.

Start by listing what you could not replace. CISA's advice for small businesses begins with exactly that inventory, and the same works at home: photos and videos, documents such as contracts and certificates, schoolwork, and the list of accounts and recovery codes you would need after losing a device. Programs can be reinstalled; those files cannot.

Why a synced folder is not a backup

Many people assume that because their files sync to the cloud, they are backed up. CISA's ransomware guide warns that automatic cloud sync may not be enough. If files on your computer are encrypted by an attacker, the encrypted versions can sync to the cloud and overwrite the good copies. A deletion syncs the same way. A real backup keeps older versions you can go back to. CISA's advice for businesses is to be able to roll data back at least seven days, and many online storage services and backup tools keep a version history for that reason. Check how far back yours goes.

Two more habits come from the same guidance. Keep at least one backup offline, for example an external drive that you plug in for the backup and then unplug, because ransomware looks for any backup it can reach and encrypts or deletes it too. Protect backups with encryption, especially ones that leave the house. And test them: a backup that has never been restored is a hope, not a plan. Every few months, pick a few files and actually restore them to make sure they open.