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Thread: File deletion

  1. #1
    4 Star Lounger
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    File deletion

    I have seen several programs that claim to completely delete files by overwriting them. One of them says "Simply put, Prevent Restore overwrites any currently unused sectors on a partition with spaces, random integers, or random characters." I must be missing something here. It seems to me that if all unused sectors are overwritten in this way, then the amount of free space on the disk will be virtually eliminated. Where have I gone wrong?

  2. #2
    Plutonium Lounger
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    Re: File deletion

    When you delete a file, it is not really removed from the disk. Windows removes its entry from the list of files, and this makes the space taken up by the file available to be used for other files. But the data are still there, until they are overwritten by another file. That's why utilities such as Recuva can sometimes restore a deleted file.

    Sometimes you don't want a deleted file to be recoverable, for example because it contained sensitive information. The utilities that you mention accomplish this by overwriting the part of the disk that is marked as unused (but that could still contain the data of "deleted" files) by zeros or by random data. This does *not* use up disk space - it will still be marked as unused in the file directory.

  3. #3
    Plutonium Lounger
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    Re: File deletion

    Also, just for completeness, overwriting the data does not completely prevent a determined hacker from recovering your deleted data.

    Each time a disk writes data to the surface there is a tiny difference in exactly where the data is written, so a tiny part of the old data will still be available to a hacker with sophisticated data recovery hardware. The only way to be absolutely sure your data can't be read again is to degauss the disk and then to physically destroy it. There are a few firms that manufacturer hard disk shredders for this purpose.

    For more information see the Wikipedia article on data remanence.

    StuartR

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    Plutonium Lounger
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    Re: File deletion

    <hr>...a few firms that manufacturer hard disk shredders... <hr>
    Wow! I'd love to see one of those in operation...

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    Plutonium Lounger Leif's Avatar
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    Re: File deletion

    Take your pick...... <img src=/S/smile.gif border=0 alt=smile width=15 height=15>

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    Plutonium Lounger
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    Re: File deletion

    Thank you very much! I need to get out more; I had never imagined this kind of equipment. Dang, look at this one! That's like a whole <img src=/w3timages/censored.gif alt=censored border=0> CPU this machine is eating. Frightening and the OSHA rules must be some kinda reading.
    Attached Images Attached Images

  7. #7
    Plutonium Lounger
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    Re: File deletion

    I saw one being demonstrated at a security exhibition in London a few months ago, very impressive.

    StuartR

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    Re: File deletion

    I've often wondered about this topic Stuart. In particular, I wonder if the precision of modern HDs might have reduced track/head misalignment, non-repeatability and magnetic hysteresis to levels below the resolution capability of the forensic technology. I guess it would not be in the interests of the "disk destroyer" companies to reveal such info, nor the data recovery arms of the criminal investigation and national security authorities to "show their hands" on this issue. <img src=/S/hmmn.gif border=0 alt=hmmn width=15 height=15>

    Alan

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    Plutonium Lounger Leif's Avatar
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    Re: File deletion

    I was hoping to see one with a recycling facility - some kind of basket underneath to catch all the 1s and 0s dropping out... <img src=/S/shrug.gif border=0 alt=shrug width=39 height=15>

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    Silver Lounger t8ntlikly's Avatar
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    Re: File deletion

    There is one right across the river from me. As they are one of my customers I got to watch it in progress as it literally destroyed several computers, servers, etc. Awesome! I thought I saw a few 1's or 0's dropping out, but safety wouldn't let me get close enough to tell for sure.
    Thanks John
    Teamwork is essential; it gives the enemy other people to shoot at. (Murphy's War Laws #39)

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