IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Organisation Remarks
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Uniform patterns such as "0000" should not be used for overwriting, but rather
patterns such as "C1" (hexadecimal, corresponds to the bit sequence
11000001). Following on from that, in a second pass a complementary pattern
(for example 3E, corresponding to the bit sequence 00111110) should be used
so that if at all possible each bit has been changed once.
The overwrite procedure should therefore be repeated at least twice, or
preferably three times, as this provides a better protective effect.
Of course, write-protected media or media that cannot be written to more than
once, such as CD-ROMs or CD-Rs, cannot be deleted and should be
destroyed.
Erasing devices
Flexible magnetic data media (floppy disks or tapes) can be erased with an
erasing device. These devices expose the data media to an external constant or
alternating magnetic field (erasure by magnetomotive force). Suitable erasing
devices which conform to DIN 33858 are listed in BSI publication 7500.
Basically the data media are reusable after they have been erased. It should be
noted, however, that data media with a magnetically recorded servotrack (e.g.
IBM 3590, Travan 4 and MLR tape cartridges and ZIP disks) are unusable
after erasure.
Erasing hard disks
If hard disks containing sensitive data are to be passed on to third parties they
should also be erased, especially if they are removed from service or sent for
repair. It should also be borne in mind that passing on "cleaned-up" hard disks
which contain only the operating system and standard software is liable to
give rise to licensing problems.
Hard disks that are to be erased should therefore undergo low-level formatting
at least. To do this, first all existing partitions should be deleted (under DOS
with the fdisk command) and one large partition should be created. Then the
entire hard disk should be formatted (under DOS with the format /U
command).
As an additional security measure, new data can then also be loaded onto the
hard disk, for example pattern sequences with the WIPE program.
If a relatively large number of hard disks (of identical type) need to be erased,
as an alternative first one hard disk can be overwritten with a pattern and this
can then be copied to all other hard disks with an image copying program.
If the hard disk is faulty, erasure by overwriting is no longer possible. The
only option is therefore erasure with an erasing device, even though these
devices are not intended for erasing hard disks. Due to the differences in the
design of hard disk drives, in particular the number of disks, no general
comments can be made on what erasure effect can be achieved. Using an
erasing device on a hard disk usually makes the disk unusable.
Destroying the data media
A simple method of destroying data media is the cutting up of
diskettes/magnetic tapes and the mechanical destruction of hard disks.
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IT-Baseline Protection Manual: Oktober 2000