It’s tempting to think that most external storage devices—whether simple hard drives or more complicated network-attached storage (NAS) units—are relatively similar because they all do roughly the same thing. However, a recent problem with older Western Digital My Book Live NAS devices highlighted that there can be large differences. In that case, hackers figured out how to cause a factory reset that wiped the entire drive of all files. (If you have one, note that Western Digital recommends disconnecting it from the Internet immediately.) Two tips: Although no one could have anticipated this particular problem, ask us before buying external storage because we may be able to recommend known good products or warn you away from sketchy manufacturers. Also, if you store unique data on an external drive, you must back up that drive just like your Mac’s internal drive or risk losing everything, like these My Book Live owners did. Backup, backup, backup!