Surprise Benefit In Zero-ing Out Unused Space

Highly security-conscious users have long recommended using a utility to write zeros in the unused areas of your hard drive, overwriting any scraps and fragments of old files there so that they can’t be easily recovered by snoops. Sometimes, the tools for doing this write multiple patterns of numbers multiple times, making recovery of the overwritten old data extremely difficult— in fact, all but impossible, except through truly extraordinary and expensive means.

This reader found another reason for doing this, too:

Fred,  Just thought I’d write to say thanks for Langalist (Plus!!)  and all that’s in it, and hopefully to pass-on a good tip for your other readers…

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Some time ago you wrote about imaging programs and pointed to several. (I already had Norton Ghost but didn’t care much for the Dos user interface) . I followed the links to Acronis and for $10, a special for Langalist customers who already had Ghost, I got True Image (v6). I’ve been using it for some time but was looking for a  way to improve the compression. My images for my 10gb Harddrive were 4+GB even after using the highest form of built in compression. I came upon an idea!:  If I could zero out all the unused disc space it should enable the compression tools to make the compressed file even smaller! I tried it out and sure enough, my latest image (after cleanup of unneeded files, temp files, defrag and zeroing out unused data was down to around 1.3GB.

BTW,  I used a freeware  program called "Eraser " to zero out the data. It is fundamentally a security program meant to write multipass pseudorandom data over a file to  completely erase and make it unrecoverable. It is also flexible enough that it can be set to write one pass of zeros over only the unused space on the disc. It still takes some time, but it’s worth it!— Chuck Brotman

Thanks, Chuck, that’s a great idea.

Some imaging tools simply skip unused data areas, but those that image the unused space could indeed benefit from this technique: The unused space will be filled with highly-compressible data (all zeros or all ones, for example), so the resulting compressed image file will squeeze down to the smallest possible space.

The major downside to this is that it can take a *very* long time to fill a large hard drive’s unused file areas this way, especially if you choose a multipass method. But it still may be worthwhile, either for the extra security, or for the smaller images that may result. You may be able to automate the process to make it work itself at night when the machine is otherwise not in use, too. Keeping your partitions down to reasonable working sizes also will help.

Eraser, and similar tools (mostly free):
http://www.thefreecountry.com/security/securedelete.shtml
http://www.google.com/search?q=security+wipe+free

Fred Langa

About Fred Langa

Fred Langa is senior editor. His LangaList Newsletter merged with Windows Secrets on Nov. 16, 2006. Prior to that, Fred was editor of Byte Magazine (1987 to 1991) and editorial director of CMP Media (1991 to 1996), overseeing Windows Magazine and others.