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From: 3ksnn64@pur-ee.UUCP
Newsgroups: sci.crypt
Subject: Re: Erasing magnetic media
Message-ID: <6980@pur-ee.UUCP>
Date: Wed, 4-Nov-87 17:40:43 EST
Article-I.D.: pur-ee.6980
Posted: Wed Nov  4 17:40:43 1987
Date-Received: Sat, 7-Nov-87 17:38:22 EST
References: <7566@reed.UUCP> <1175@cup.portal.com> <6964@pur-ee.UUCP> <1029@pbhyd.UUCP>
Reply-To: 3ksnn64@pur-ee.UUCP (Joe Cychosz)
Organization: Purdue University Engineering Computer Network
Lines: 13

In article <1029@pbhyd.UUCP> lc@pbhyd.UUCP (Larry Colton) writes:
>>It is quite easy (given the proper equipment) to recover information that
>>has be written over several times.
>
>Could you enlighten us with the details?  There is great commercial
>potential in being able to recover files that have been accidentally 
>overwritten.
>

There is a residual of the original data still present.  Small signal
analysis can be used to recover the original data.  Obviously the more
times the tape is written over, the harder it is recover the intended
data.