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Why file removal tools offer gost 2 passes and British 3 passes or even gutman 35 passes options? In which case the single pseudo random pass is not enough?

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  • $\begingroup$ the magnetic coding used to store the data may still contain some remainders after a single pass which may be exploited by a dedicated attacker. Multiple overwrites fix this. Modern drives don't need many due to high data density, older drives (at the time Gutmann's method was presented) were smaller and less dense, meaning more passes were required. $\endgroup$
    – SEJPM
    Oct 12 '15 at 16:38
  • $\begingroup$ I'm closing question as off-topic because it is a question about physical security, not about cryptography. $\endgroup$ Oct 12 '15 at 17:29
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    $\begingroup$ Information Security has several questions about erasing disks, including How can I reliably erase all information on a hard drive? and Disk Erasing Security - Odd Number of Writes. If none of them answers your problem, you could ask again on security.stackexchange.com. $\endgroup$ Oct 12 '15 at 17:31
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This has to do with the physical nature of the storage device. Simply deleting the reference still leaves the data available for recovery. Writing once over randomly might still leave chunk traces of data which could be pieced together.

It is not generally considered easy to recover information overwritten once, and for your own pc... being donated or sold... once is probably enough. Depending on your own scale of paranoia you can use more passes.

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