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How to securely delete files

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Secure file deletion: erase files and folders

What is secure file deletion

PeaZip, Open Source cross platform file manager for Windows, macOS, and Linux, provides"Secure delete" function in context menu and in "File tools" submenu.
The secure deletion function is intended for permanently remove file and folders erasing data in a secure way, overwriting multiple times disk sectors where information is stored; such function is also known as file shredding, or data erasure.

This is a permanent and unrecoverable deletion of data, not allowing any recovery of erased information from disk - similar to eraser software like SDelete or CCleaner.

It is not possible to recover securely deleted data

Use secure file deletion very carefully, since permanently deleted data will reasonably be not recoverable with known - hardware or software - data recovery tools.

What is non-secure file deletion

Non-secure deletion, as usually implemented on most operating systems, is a plain de-referencing of the file name in the file system allocation structure, leaving unaffected the data stored on disk until it is, by chance, overwritten by new data.
This allows information to be recovered by data-recovery softare until not overwritten with fresh data, otherwise specialized hardware recovery tools can be used to scan the surface of the disk (or memory cells) to detect with a reasonable range of certaininty up to a few previously stored states in the same memory unit, even is setctors / memory units were overwritten (a few times) with fresh values.

How does PeaZip perform secure data deletion

PeaZip's secure data delete utility accepts multiple files and/or directories as input and provides multiple overwriting of file data with random data stream (original data is replaced by an AES256 CTR -generated random stream) forcing flush to disk each time, then replacement of content with randomly sized random data to fake file size, and multiple renaming of the file with random string.
PeaZip freeware file manager / explorer can find files to be securely deleted querying the filesystem with its own custom functions, based from low level primitives rather than relying on operating system's high level file browsing API; that (in some instances) enables the program to show data otherwise not visible - not simply hidden, but otherwise purposely protected or made not accessible to system file manager, by the operating system itself or even malicious software.

At current level of development however, PeaZip secure deletion utility cannot unlock files locked by other processes (requires to find and kill the process locking the file) in order to remove undeletable files - this has be done separately by dedicated, system-specific utilities.

Limitations of secure file deletion
Please note that secure file deletion doesn’t overcome all known risks of data leakage, since may exist copies of the data as temporary files saved by application that accessed the file, or as not securely deleted older version of the file, or cached by the system: clearing a file cannot affect that orphaned data, which can be recovered with suitable software utilities or specific hardware probes.

Secure delete on flash based storage

Flash units (as solid state disks SSD or USB keys) usually re-allocates sectors for writing transparently for the software, in order to reduce unit’s wear since flash units have a shorter lifespan in terms of writes; this doesn’t allow to efficiently wipe and physically overwrite original content, reducing the efficiency of file shredding.
In this case only erasing the entire disk (with one or more random data passage on all the free space) would be effective to securely erase remnants of data, but this can be very time consuming and, for flash based or hybrid drives, it will lead to fast wear and reduced lifespan of devices.

Secure delete on cloud and remote storage

Data stored on remote servers (as in cloud services, even freeware ones) may be subject to periodic backup unknowingly to users, so please consider that copy of the data before erasure may exists on servers, out of the reach of users, if such services are employed, unless differently specified in terms of service.
Moreover, as terms of services are often subject to variations, and limitations in user's rights depending on the laws applying to the provider of the services (such as, possibly, do any effort in providing access to user's data under some circumstances), it is highly recommended encrypting data on user's end before upload to any external machine, even when encryption (or user data erasure) is offered as service by the remote storage / cloud service provider.

Quick delete function

"Quick delete" is provided as an alternative to secure deletion by PeaZip file manager, this action deletes files and folders without moving data to the recycle bin, which is faster and increases security against forgetting of recycled data.
Like secure deletion, fast deletion does not allows to recover data from the system's recycle bin, and in this sense it provides a simple way to permanently erase data, but this procedure is not intended for securely sanitizing data: as no data overwriting stage is involved in the process, it is feasible to recover data destroyed with fast delete using appropriate undelete utilities.

How to securely delete free disk space

Securely delete free disk space

Secure delete is also available for free space: the free disk space on the specified unit is physically overwritten multiple time with a random stream as in secure file deletion tasks - it may take several minutes to wipe large disks - likewise software as OS X Disk Utility to erase free space, or cipher /w command in Windows.
In this way leftover remnants of data previously saved to disk (deleted files, reallocated sectors, ...) are wiped and replaced by random data generated by the disk eraser program, making analysys of free space useless.
This level of security is not matched by formatting the volume, as quick format routines does not overwrite existing data, which can be recovered with specific utilities, and even more through format utilities does not implement a multi-pass overwriting of free space with random data, making previous state of the disk recoverable with suitable hardware scanning equipment.

Zero delete free space

Zero delete files and free space is also available, the function overwrites data with all zeroes before deletion. It is recommended to be performed before saving disk images either of physical machines (for backup and disaster recovery) and for virtual machines' disk images, as more uniform (zeroed) data is much more easily compressible - learn more optimizing virtual machines and disk images backup - but it is not recommended when it is needed to sercurely erase disk content so it becomes unrecoverable by specialized data recovery (undelete) software.
Windows system, from Windows 7 onward, zeroes bytes on drives when performing full format, while quick format simply de-reference the files without overwriting leftover data traces.

Read more about secure data deletion: data erasure

, and data recovery

Wikipedia entries, disk sanitization software examples: OS X Disk Utility freeware apple os x disk utilities

, and Microsoft cipher /w overwrite deleted files

command.

Learn how to securely share files on email or cloud, how to create backup copy or how to save files and folders to a 7z, rar, tar, zip archive, and how to protect data against accidental deletion or aunauthorized access.

Synopsis: How to use PeaZip as freeware Open Source cross platform data deletion utility for Windows and Linux. Secure deletion of files and folders (file wipe). Secure deletion of free disk space to erase (sanitize) media supports.

Topics: secure file deletion utility, securely delete free disk space, permanent removal of data, erase supports

PeaZip > FAQ > Free, Open Source secure delete utility