Secure Erase Seperating Fact From Fiction...

Hello World!

Can someone tell me if the following statements are fact or fiction...

1) After you overwrite data, there still remains a "ghost" of the original image so when erasing data, you must overwrite the sectors multiple times to "really" erase the data.

2) A low level format makes sure that no data can ever be retrieved from a hard drive.

I am writing a hard drive purging software that simply opens every free block of a drive and will write all "0"s into them and then all "1"s into them.  To clear the the TOC entries without having to reformat, I create a large number of empty files in a hierarchical tree structure and then I delete those files once done.  Is this a waste of time?

-- Bubba
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Christopher McKayConnect With a Mentor Microsoft Network AdministratorCommented:
As stated by mcp_jon the first one is definitely a fact. Using recovery software such as (GetDataBack) it's possible to recover data from drives that have been deleted, or even from a drive that's been formatted/ fdisked etc.

The second I have a bit more difficulty agreeing with. It's working off of a "If you write 0s across the drive, it will be empty". Strictly speaking, this isn't necessarily true. The reason behind this is that when data is written to the drive, the magnetic head travels aroud the platters in a circular pattern with the head moving back and forth across the disk. The heads follow a "path" similar to a CD track. This "path" is wider than the magnetic heads, which allows small amounts of movement within the "track". What this ultimately means, is if when writing to the disk, the heads are on the "outside" of the track, and then when doing a low level format (which is unadvised for newer disks) the heads are on the "inside" of the disks, it is still possible to catch the data that was written to the disk by reading the "outside" edge of the track. Data Recovery Specialists use special tools to accomplish this.

Disk wiping software uses multiple writes across the track to ensure that the different areas are all overwritten. I use DBAN to do disk wipes. ( The problem with this is it take a long time to wipe a disk.

Ultimately, the question is how important is it to you that everything be totally gone? If it is very very important, I would recommend destroying the hard drive rather than trying to clean it. If it's just a desire to make it next to impossible to get anything off the drive for most people, I'd recommend DBAN.

I work for the Canadian Government, and our policy is quite strict surrounding this issue... we're permitted to use DBAN, so it meets their standards, which hopefully will be good enough for you as well.

Hope this helps!


mcp_jonConnect With a Mentor Commented:
1) Fact - Overwriting time and time again makes the chances of getting info back really dificult, but it can be done.
2) Fact - The so called "Low-Level" is very well explained here " "

Is this a waste of time?
Only regarding that there are a lot of good free programs to do the same, but Hey, another one is also well received... So PLEASE don't stop what you are doing.

If you need further assistance, just ask !

Best Regards
bganoushAuthor Commented:


I just had to comment... not about your answer but because your ID is "Bartender" and you work for the Canadian Government...  You're proliferating the myth that the country is run from a pub... now what will americans be thinking???

Anyway, thanks for your answers.  I work in a "Privacy" scenario where someone might sue us for leaving a data trail. Because some hardware doesn't come cheap, we prefer to flush the data before destoying the media. In some cases, people are just too hung up on the issue but I have been deligated to erase what I can.

I did have a suspicion that the head could "travel" across a track but I also thought that there was a certain amount of overlap between tracks where the data from both adjacent tracks are blended to a point where you really couldn't tell what the original data was... It makes more sense as you put it that there is no overlap but in fact that the data is written loosely across a track.

In any case, thanks.
Christopher McKayMicrosoft Network AdministratorCommented:
My online name of "Bartender_1" stems from many years ago, when I used to work as a bartender, but I appreciate the humor. ~LOL~

I'd recommend you check out DBAN, use it on your disks, and then try to get the data off of the disk. use whatever means you wish, and see if it meets your standards.


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