Mark Jenkins

Information Technologist


Are your backups safe from your backups?

People keep backups so they can recover data if it is lost or altered. They imagine how relieved they will feel if a disaster wipes out their original data but the information is safely stowed somewhere else.

But, how safe are your backups?

Often we don’t think we’ll be unlucky enough to lose both our original and backed up data at the same time. Or we think that the disaster is so unlikely that we are willing to accept the potential consequences, especially if the data isn’t that important. For example, a fire in your home could wipe out a music collection in your den and the backup in the basement. However, if that happens, you’ve got bigger problems than some missing mp3s, so you’re willing to take the risk.

In that scenario, both copies are lost because you put them in the same building. They had a common link — location — that gave them a common fate. It was obvious that the disaster was possible all along.

Often, however, we compromise our backups by linking them to our originals in ways that aren’t obvious.

Consider the popular storage service Dropbox, which is said to have 175 million users. They provide a folder on your computer that is automatically synchronized with an online copy managed by Dropbox (or you can access it through the web).

A malicious person who has access to your computer can delete or deface the documents, and these changes will be backed up to Dropbox as well, erasing the original. This could be someone breaking into your premises, your disgrunted employee-nephew, or malware. The problem here is that the very location where the original data is stored also has access to the backups.

With systems like Dropbox, you can discover just how easily your files can be compromised, because by directly interacting with the software you realize that your own changes and deletions show up in both the original and backup. It is clear that someone else sitting at your computer could do the same. (You also realize that Dropbox doesn’t protect you from your own mistakes.)

Other backups schemes have the same problem, but are less transparent to the user. Many popular schemes available today are automatic, run overnight, and quietly copy your data to an offsite location.

What you may not realize is that the qualities that make such a scheme convenient also make it more dangerous.

To run automatically, your computer has to retain login credentials for whatever online storage service is being used.  Those credentials can be used for their intended purpose, or for a malicious purpose – to log into the backup service and delete your backups while also deleting the original on your computer.

There’s a naive solution to this problem: configure the backup system to only transmit file changes, never orders to delete.

No problem. As your malicious babysitter Rupert, I will just change the 200 page thesis that you have both on your computer and on your backup service to the following one-line poem: “There once was a man named Foobar”. Then I’ll trigger a re-run of the backup routine (or just wait for it to kick in automatically at 2am if I’m lazy). Now we have an original and backup copy of my work work and no copies (original or backup) left of your thesis. I’m sorry.

This could still be a problem if you do manual, local backups with something like a USB drive. If your data is damaged and you manually back it up on on top of your backup copy, then you’ve got two copies of garbage and no copy of a good version.

Keeping multiple versions of the whatever you work with on the same portable drive might not save you from this either. Let’s make this Hollywood and consider a high stakes industrial sabotage scenario. You’re an engineer at Small Lab Inc. and are designing Titanic II. Every time you start a major revision, you copy and rename your design file to reflect your new version, e.g. “titantic_II_v35.svg”. As you finish for the day, you pull out your USB drive and add this new revision to your set of backups.

Too bad that Larry, the polite intern with keys and overnight access, installed a malware program that triggers when your USB drive is connected. His malicious program goes after all of them, titantic_II_v1.svg, titantic_II_v2.svg… titantic_II_v35.svg, both on your main drive and backup drive. He replaces all of them with Nyan Cats. All of them.

If you’re very lucky, he at least retains his own copy of the originals for extortion purposes, or says, “Happy April Fool’s Day! Here’s your file back.”

There are two things to take away from all of this:

First, you must have multiple backup copies of your files.

Second, you must isolate all your other backups from the process by which your latest backup takes place.

If you’d like to avoid ending up with all Nyan Cats, I can help. I can evaluate your existing schemes and implement new ones.

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