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[[!meta title="Securely deleting files and clean diskspace"]]
[[!toc levels=1]]
[[!toc levels=1]]
<h1 id="why">Why use secure deletion?</h1>
Warum sicheres Löschen verwenden?
**Operating systems do not actually remove the contents of a file when it is
deleted**, even after emptying the trash or explicitly removing the file, from
the command line for example.
Instead, they simply remove the file's entry from the file system directory, because this requires less work and is therefore faster. The contents of the file—the actual data—remain on the storage medium. The data will remain there until the operating system reuses the space for new data.
Likewise, reformatting, repartitioning or reimaging a system is not always guaranteed to write to every area of the disk, though all will cause the disk to appear empty or, in the case of reimaging, empty except for the files present in the image, to most software.
Finally, even when the storage medium is overwritten, physical properties of the medium might make it possible to recover the previous contents. In most cases however, this recovery is not possible by just reading from the storage device in the usual way, but requires using laboratory techniques such as disassembling the device and directly accessing/reading from its components.
To learn more, see the Wikipedia article on [[!wikipedia Data_erasure desc="data erasure"]].
<h1 id="usb_and_ssd">Warning about USB sticks and SSDs</h1>
<div class="caution">
<div class="caution">
<p>Secure deletion is not as reliable on USB sticks and SSDs (solid-state
drive) as it is on traditional hard disks.</p>
USB sticks and SSDs sometimes copy the same data to various memory cells to extend the lifetime of the device. USB sticks and SSDs also have 10&ndash;20% of spare memory cells for the same reason.
As a consequence, part of the data from a given file might still be written on the device even after securely deleting it.
This data could be recovered using advanced data forensics techniques, for example by professional data recovery services.
To mitigate this risk, you can:
- Encrypt the device before use, to make it hard to recover *any* data.
Securely delete the entire device. Some old data might still be present in the spare memory cells.
- Physically destroy the device.
<h1 id="files">Securely deleting files</h1>
Dateien sicher löschen