Re: [Full-Disclosure] Erasing a hard disk easily

From: Maarten (fulldisc_at_ultratux.org)
Date: 07/12/04

  • Next message: amilabs: "RE: [Full-Disclosure] Erasing a hard disk easily" 
    To: full-disclosure@lists.netsys.com
Date: Mon, 12 Jul 2004 23:23:24 +0200

    On Monday 12 July 2004 21:27, amilabs wrote:

    > I have a bunch of old computers I would like to donate. Old laptops with
    > win 95/98 on them and some old tower desktops all circa 1995-2k.
    > I would like to know if I can just use a magnet to completely wipe out the
    > data for obvious security reasons. I have heard about the disk erasers like
    > active kill and Perl utilities for this but with the ability of data
    > ghosting etc. is this enough? Can I use a big magnet like a speaker magnet
    > or something like a degasser to just wipe out the data without having to
    > boot these old boxes and go through all the extra work.

    Um, yes and no. Actually: No (for what you want to accomplish).

    No you cannot use a big strong magnet. In fact, a _very_ strong magnet is
    already inside each drive, as part of the actuator coil assembly that moves
    the head. I'm not kidding, those are real strong magnets. Barely can't get
    them off my refrigerator. (no, really...) :-)
    To get a magnet close enough to the surface to be effective you'd need to open
    up the drive and that spells certain death for the device. And even then, to
    erase you need an alternating magnetic field, a static one (from a magnet)
    will not erase anything. Or, at least not with feasible field-strengths...

    In the meantime, there are industry bulk erasers available that alledgedly
    also can handle drives (they're quite pricey!). But their use is solely for
    destroying data AND drive together; as the drive is totally wiped, the servo
    tracks that the factory installed are also gone. Without them, the drive is
    utterly useless, and servo tracks can only be (re)written at the factory.

    So, if you want to erase the data but keep the drives operational too, you
    have but one means left: by plain old formatting. Depending on the level of
    security you want, you can opt for:

    * DOS/Windows format (beware: this does not erase ANY data at all !!)
    * Low-level format / wipe (with special tools, level depends on the tool used)
    * Linux dd overwriting using /dev/zero (fairly good if used multiple times)
    * Linux dd overwriting using random data (excellent if used multiple times)
    * Department-of-defense level (dd as above but lots more times (like 10+))

    An overwrite with all zeros will -allegedly- not withstand a serious
    data-recovery attempt by professionals, not even when repeated.
    An overwrite with alternating zeros and ones will defer almost anbody, and so
    will a random-data overwrite, provided both are repeated at least 3-5 times.
    A single wipe with ones is not effective against determined people.
    But all of the above will still defer an amateur (without funds). And a DOS
    format will not defer anybody except newbies, nitwits and idiots. :-)

    [ the command for dd overwrite with zeros is: dd if=/dev/zero of=/dev/hd? ]

    Good luck with it.

    Maarten 

    -- 
Yes of course I'm sure it's the red cable. I guarante[^%!/+)F#0c|'NO CARRIER
_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.netsys.com/full-disclosure-charter.html
  • Next message: amilabs: "RE: [Full-Disclosure] Erasing a hard disk easily"

    Relevant Pages

    • Re: [Full-Disclosure] Erasing a hard disk easily
      ... I know we're always looking for new targets, box up the drives and ... I would like to know if I can just use a magnet to ... > completely wipe out the data for obvious security reasons. ... "Communications without intelligence is noise; ...
      (Full-Disclosure)
    • Re: A new use for Linux
      ... >> A straight magnet can mess it up a bit, but I don't know about total ... Generally degaussing takes an AC field, ... The newer platters are much harder as we found out when we tried to cut ... I was going through some old drives and destroying them. ...
      (Fedora)
    • Re: Erasing a Drive
      ... Magnetic coating in modern drives is only thick enough to hold one domain... ... regular black ferrite magnet which gives stronger ... into the magnatice noise as newer data overwrites and blends the ...
      (comp.sys.ibm.pc.hardware.storage)
    • Re: Fraudsters stealing personal details from discarded computers
      ... Just run a honking fat magnet over the drives ... this gets hairy only if there are a large number of disks, ...
      (soc.retirement)
    • Re: Hard drives v. CF/Smart media/etc.
      ... a magnetic platter. ... Probably won't do anything to flash media. ... goes for the newer USB Hard Drives as well. ... You cannot use a magnet to erase a hard ...
      (Security-Basics)