Deleting data from a computer It is a sensitive task. So much so, that when the US decided to withdraw from Afghanistan, the Department of Defense issued a report with the guidelines to follow to prevent data from falling into the hands of the Taliban. The military withdrawal from the Asian country is obviously an extreme and heroic situation. It is also a resource sometimes used to destroy evidence of crimes or compromising photos. But the vast majority of the time it is the procedure that companies and individuals use before recycling a computer or giving it away or giving it away. In all these cases, simply deleting the data is not enough, and expert hands could recover the information without problem, says Juan José Galán, head of business strategy at All4Sec.

“Formatting a hard drive is not enough,” explains Galán. “We tend to think that if we reformat the hard drive of a computer, it will be configured in its original factory installation and all the information will have been eliminated. However, nothing could be further from the truth ”. The expert explains that reformatting a computer’s disk only leads to the file index tables disappearing, but not their content. “It will be practically the same as deleting a file and forgetting it in the recycle bin.” Thus, with suitable tools it will be possible to retrieve the content and access it almost immediately.

That is, when we delete a file and free up memory, the computer simply marks that piece of memory as available, but the file itself is actually still available. What is the proper standard procedure? First of all, you do have to proceed to the classic hard drive formatting. But it is also essential to overwrite it several times. When a user saves a file, the system does not archive it as a single piece, but fragments it into several pieces, so it can happen that with a single overwrite, pieces of a file remain without deleting. This option cannot be used on those that are damaged or those that are not rewritable, such as CDs and DVDs.

An example: if we have a 500GB internal hard drive, we will format it first. Subsequently, we must copy and paste a large file (for example a 5gb movie) 100 times to fill the capacity. Afterwards, we must not forget to empty the recycle bin. “And if the disk is reformatted and done a second time, the better,” says Galán.

There is a second option, which involves degaussing the hard drive. Those who have seen the series Breaking bad They will remember the first chapter of the fifth season, in which Walter White and Jessie Pinkman used a giant magnet to demagnetize the incriminating content of a computer guarded by the police. Something similar can be done on a smaller scale. Demagnetization consists of exposing the media to a powerful magnetic field, a process that eliminates the data stored on the device. Each device, depending on its size, shape and the type of magnetic support in question, needs a specific power to ensure the complete polarization of all the particles, as explained by the National Cybersecurity Institute (Incibe).

These two procedures, overwriting and degaussing, do not destroy the media. The most expeditious way to eliminate the information is the destruction of the medium. In fact, “in optical and electronic discs, such as DVD, CD or solid hard drives (SSD), only physical destruction guarantees the elimination of stored content,” explains Juanjo Galán. “But even for destruction there are conditions. The normative UNE-EN 15713: 2010, Safe destruction of confidential material, code of good practice, it collects up to eight levels of crushing or disintegration ”, emphasizes the expert. There are formulas such as disintegration, pulverization, melting or incineration, all of them to completely destroy the storage media. “These methods are usually carried out in a metal shredder or an authorized incineration plant,” warns Incibe. Shredders can be used to destroy flexible storage media, such as outdated floppy disks. Optical storage media (CDs, DVDs, magneto-optics) must be destroyed by pulverizing, cross-cutting shredding, or incineration.

And what happens in the case of mobiles? These devices are a separate case, explains Galán. Its content is encrypted, so a factory reset is usually sufficient. This, in any case, applies only to the internal memory of the terminal. If the phone has a SIM card, it will have to be overwritten so that the content is out of the reach of third parties. “It should be remembered that technological obsolescence is an irreversible process. Sooner or later devices get old and we can all make mistakes when we get rid of them. “

You can follow EL PAÍS TECNOLOGÍA at Facebook and Twitter or sign up here to receive our weekly newsletter.