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Old 02-16-2005, 10:30 PM   #1
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best way to get rid of files? (for good)

I have recently tried a data recovery on a formatted HD.
while reading on the topic, I found interesting that, one one side, people say it's very hard to recover the files and, on the other, people affirm that there is no such thing as a secure delete.
I found that many "experts" say that overwrting files due to lack of space makes the recovery harder than a full format.
I would like to hear opinions about what would make recoverying files harder in the case we want to get rid of them.
what tools and techiniques are employed in data recovery?
also i would appreciate suggestion of further reading and howto's.
Old 02-16-2005, 10:57 PM   #2
Registered: Feb 2002
Location: IL
Distribution: Ubuntu currently, also Fedora, RHEL, CentOS
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Scrubbing disks with a magnet is always good, but if you want to keep a filesystem or parts of the disk you can use dd.

I sometimes will do a

$ dd if=/dev/zero of=/path/to/file/I/want/deleted

that zeros it out, then delete it.

You could also use /dev/random.

Most security experts say you need to format/overwrite data 7 times for it to be non recoverable. You can write zeros all day long pretty easily.

Old 02-16-2005, 10:58 PM   #3
Registered: Aug 2003
Location: Melbourne Australia
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I have done a few experiments with this using a single floppy disk.

I wrote a simple text document and saved it on the disk, then i formated it.

using grep, i was able to recover some information off the fdd.

to wipe the disk completely, i perfomed a dd if=/dev/zero of=/dev/fd0
this overwrote the entire disk with zero's.

I could not rcover any information after this, and i would think hardly anyone could
Old 02-16-2005, 11:00 PM   #4
Registered: Jun 2003
Location: Denver, CO
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The Free Software Foundations 'shred' (man shred) is on my slackware box by default, but you can get it for free if it's not on yours. That'll delete anything well enough that only the NSA or some entity with similar resources could get it back. And I personally doubt even they could. I think this stuff about 'no such thing as a secure delete' is FUD.

Of course, I'm ignoring temp files, caches, tempest attacks, and other operating system issues.

Last edited by jlangelier; 02-16-2005 at 11:01 PM.
Old 02-16-2005, 11:41 PM   #5
Registered: Oct 2003
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There is also a program called dban that I use from time to time before selling a hard drive. But if you truely want it gone then Thermite comes to mind, or maybe an acetylene torch.
Old 02-18-2005, 12:39 PM   #6
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thanks everyone for the feedback.
it seems it's easier to make a secure delete zeroing the entire HD, although this is less useful for the normal user who want to just erase some information and keep using his PC.
I read that file fragmentation is also a factor in a succeful recovery.
especially on windows systems, a frequent defrag will make recovery easier.
I think I'll head for a flee market, get myself a used HD and hack the hell out of it.


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