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Special Cases
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| You can safely erase files compressed at the file system level (file compression requires a file system that supports it, such as NTFS). When erasing compressed files on Windows NT or 2000, Administrator privileges are required for low-level disk access.
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| Files compressed with an external application, such as ZIP files, can naturally be erased.
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| If you are erasing files from a partition compressed with external compression software (such as DriveSpace), use only pseudorandom data for overwriting.
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| Files and unused space on a compressed NTFS partition can be erased normally.
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| However, if your partition is compressed with external compression software (such as DriveSpace), the following details should be considered. In general, one should avoid storing sensitive data on a partition compressed with external software.
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| Turn off cluster tip erasing for partitions that are compressed with external software, erasing cluster tips will confuse the application that handles the compressing and may result to dramatic loss of disk space. If you erased cluster tips on a compressed drive and lost significant amount of disk space, you must recompress the drive to restore the lost space.
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| You should use only pseudorandom data when overwriting unused space on a partition compressed with external software, the other methods include passes that are of highly compressible data and should not be used. Your computer may slow down and even stop responding because the written data is being compressed.
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| Files saved on the compressed drive can also be overwritten taking the aforementioned matters into consideration.
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| You can safely erase files encrypted at the file system level (file compression requires a file system that supports it). Files encrypted with an external application, such as Pretty Good Privacy (PGP), can be erased as well.
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| As the data is already stored in unreadable format, erasing is not required, but usually increases security.
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| In general, one should not erase the unused disk space on an encrypted drive (the same applies to encrypted virtual drives, such as the ones created by PGPDisk, ScramDisk or E4M).
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| The erasing will be useless because the data saved on the drive is encrypted into unreadable format, erasing may slow down your computer and it may even stop responding, depending on the driver that handles encryption.
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| Files on the encrypted drives can be overwritten, but this should be avoided because of the reasons mentioned above.
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| You should never erase data from a drive over the network. It will not work as expected and your network administrator will hate you for jamming the network.
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| You can erase data on a floppy disk just if you were erasing a hard disk. However, if you have stored sensitive data on a floppy disk, you may want to consider physically destroying the disk using another method, such as burning it.
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| You should not use multiple overwriting passes to erase data on a CD-RW or DVD-RAM disk (or another rewritable optical media). These are not magnetic media and overwriting multiple times would have no meaning, if you want to erase a single file, one overwriting pass is enough. Use the CD-writing software to format the disk when you want to clear its contents; or if the disk contains sensitive data, you may want to consider physically destroying it by possibly shredding or burning the disk.
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