All the personal data concerning you is stored on your computer, and more specifically on the hard drive. If you plan to sell it, reuse it or give it away, it is important to make sure your storage media is properly erased. Permanently deleting data is relatively easy on most hard drives, in order to protect your data and prevent it from being recovered by someone with bad intentions. How this is done depends on the operating system used and the type of storage device the computer is equipped with.
What does permanently erasing personal data from a drive involve?
Most users think they can delete a file or folder simply by placing it in the operating system’s recycle bin and emptying it. This is not the case, because when this method is used, the file always remains on the hard drive. In fact, a great deal of information is recorded on the hard drive, and it is referenced in a special table which the system accesses when it needs to open the documents requested by the user. When a file is deleted by emptying the recycle bin, the file system tells the operating system that the space used by the document is free, but the file remains there until the reserved space is overwritten by another file. Consequently, permanently deleting data stored on a hard drive means writing information randomly and, if possible, repeatedly, into the memory space where the data to be deleted is stored.
How to permanently delete data from a hard drive?
As we have already mentioned, the best way to permanently delete data from a storage medium is to overwrite it. Depending on the type of hard drive you have, you can opt for certain erasure methods, including reinstalling the operating system or using third-party data deletion software.
Mechanical Hard Drive (HDD)
The process of erasing a mechanical hard drive involves overwriting the data. You can use the PC reset option, which consequently deletes the data on the hard drive. If you simply want to recycle, give away or sell your computer, the restore function makes data recovery much more difficult, especially if the data is also encrypted. If you are on a Windows operating system and want to erase your files:
- Go to “Settings”, then “System”, then “Update & Security” and finally “Recovery”.
- Click “Reset PC” under “Reset this PC”
- Select “Remove everything” (if you don’t want to wipe your computer, you can use “Keep my files” to thoroughly clean your computer and improve its performance).
You also have the option of permanently deleting your data using erasure software. What these erasure utilities have in common is that they all rewrite passes (binary ones and zeros) onto the drive you want to clean, and they do this several times in a row. The goal of this method is to make the stored data inaccessible. To use these data erasure utilities, you need to download them onto a USB drive and run them from there.
Another data erasure method for a storage medium is degaussing. Degaussing is a process for erasing a magnetic-media hard drive, based on magnetic fields. During this process, a powerful magnetic field is created (more than 10,000 gauss) which neutralizes the information present on the hard drive.
SSD Hard Drive
If you bought your computer in the last few years, you probably have an SSD drive. This type of hard drive is faster than older mechanical hard drives and uses flash memory instead of magnetic media. However, the drawback of this technology is that it is very difficult to securely delete files from an SSD. SSDs use a technique called “wear levelling” to extend their lifespan. However, a side effect of this process is that confidential data can remain on the drive even after it has been erased.
So instead of erasing the contents of SSDs with an erasure utility, it is better to encrypt them. This involves manipulating the data using a mathematical process and a key that only you know. Without this key, the files on the drive appear as garbage. Even if someone manages to recover the files after they have been erased, they will not be able to restore them.
Is it possible to recover confidential data deleted by mistake?
The various methods mentioned below can be used for permanently erasing data. However, it can happen that while using one of these methods, data is accidentally deleted from the hard drive. Although these methods are based on overwriting the drive, it is still possible to recover some of the deleted information. Indeed, even if you erase the hard drive and overwrite all the deleted files, traces of the original data remain. Writing to a magnetic medium is not as precise as one might think; when a file is overwritten, the new version does not completely cover the old one. The remaining information can be read using certain data remanence techniques used by data recovery professionals. It is therefore possible to recover confidential data deleted by mistake. However, it is worth knowing that these recovery techniques can also be used by malicious individuals to recover your personal information. The only way to make data unrecoverable is to physically destroy the hard drive on which it is stored. This way, you can be assured that no software can be used to recover your sensitive data.