What happens if my files are corrupted on my home computer and then they are backed up? Will the backup also be corrupted?

Posted by kent on November 24th, 2009

The following post in our Reader Question series is an actual user submitted question. To maintain the integrity of the original question, we do not edit or change reader questions in any way.

What happens if my files are corrupted on my home computer and then they are backed up? Will the backup also be corrupted?

A: It depends on when your files became corrupted, when they were last backed up, and what kind of backup history your online backup provider maintains. Your online backup software will back up your data as-is, preserving any file corruption (just as it would preserve a deleted sentence in a Word document). Now, if you backed up on Saturday, and the files were corrupted on Sunday, you could simply restore the files from Saturday's backup. But what if your backup ran after the files became corrupted? What if your service backs up a file any time it's changed?

There's hope. Most online backup services such as Carbonite, SugarSync, Mozy, and IDrive offer "versioning" (sometimes called "history" or "time-line restore") meaning they save copies of different versions that you've backed up, essentially allowing you to go back in time. Here's how Carbonite works:

Carbonite will save one version for each of the previous seven days, one version for each of the prior three weeks, and one version for each of the prior two months.

So, it's possible you may be able to access older, uncorrupted versions of your files. The amount of time older files are kept depends on your service (Mozy, for instance, keeps 30-days worth, while Carbonite keeps three-months worth, and IDrive keeps the last 30 versions). You should check the individual help section of your service provider for details.

Also note that if the corruption occurred because of a virus, you should make sure you're running Internet security software and that your virus definitions are up to date. Do this before you restore your files, so you don't risk re-corrupting your backups.