Removable device

(You can read more at http://www.chrisgreaves.com/backups/backups.html)
The important thing about a backup is that the backup device is not held on, in, at, or near the computer system.

If your back device is a second hard drive bolted into your computer, when your computer is stolen, catches fire, is trashed by a virus or befalls any similar misfortune, your backup drive goes with it.

A removable device is a backup. An internal device is not a backup.

If you are paranoid and live near an airport, you'll store your backups a mile or so away. "I can survive a "plane crash". Otherwise you'll keep your backup in a separate room. Why? Because the world is full of idiots like me who react by reaching for the backup and repeating the same idiotic action that got my main data into trouble in the first place. Keeping the backup in a separate room gives me a few extra seconds to contemplate what I'm about to do.

I have always been served well by sitting down and thinking before restoring files.

If you are backing up to a removable device and storing that device away from your computer, that's a good start.