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How to thoroughly wipe all data from your devices

Prevent data recovery on sold drives

Nothing lasts forever – especially not in the realm of hardware. If your Smartphone, Tablet or hard drive has long passed its prime and you have already made plans to sell it, you should make sure to thoroughly delete all data first. Here's how to do that for each individual device.

A study from 2012 found that a whopping 65% of all second hand hard drives are sold without scrubbing the data on it. While this might seem like a minor mishap at first, it actually poses a serious security risk for the seller if the device falls into the wrong hands. After all, any decent recovery tool can easily retrieve sensitive files containing social security numbers, passwords or bank account information within minutes. To prevent that from happening, its a good idea to consult specialized removal programs that can securely wipe possibly compromising information from your hard drive, laptop, smartphone, tablet, USB stick or SSD. Here's how to use them and what to keep in mind for each device. See also: How to clean up your PC for maximum performance

1. How safe are the standard deleting options?

Depending on the operating system of your soon-to-be-sold device, you might not need to resort to third party tools to do the job. That's why, in this section, we'll give an overview of the all the deletion options offered to users by default and explain how viable they are. If you want to jump straight into the action and see how to erase your files with dedicated tools however, head on to page 2 of this guide.

Deleting files while in Windows: It is common knowledge that Windows makes use of a two step deletion system: Redundant files first make their way into the recycle bin, typically located on the desktop, and can subsequently be irreversibly thrown off the system from there. What many users are not aware of however, is that this method actually doesn't delete the file from your hard drive at all – it just deletes all references to it.

This is due to the so-called “Master File Table” (MFT) of Windows, which is a hidden index that links files to their dedicated position on the hard drive and could thus be described as the table of contents for the whole partition. If the recycle bin is emptied, Windows turns to the MFT and simply removes the corresponding entry for the deleted files, thus losing access to the data without actually bothering to delete it.

While this form of deletion is quick and user-friendly on the one hand, it is easily reversible on the other one: Freely available recovery tools like Recuva can skim through the long stream of unreferenced data and re-establish “lost” files in a matter of minutes. Therefore, don't be lured into a false sense of security by emptying your recycle bin and always make sure to additionally clean up your hard drive with a more thorough approach.

Formatting with Windows: While relying on the Windows UI to ensure the safe removal of your data is a disaster waiting to happen, the formatting function is quite a different matter. Depending on which option you choose and what operating system you work with, it can either eradicate any trace of your data forever, or leave it lying on the hard drive in the same manner as the recycle bin.

By initializing the Windows formatting function, you will first get to choose from two different methods: Quick format and full format. The former is quite useless for our case, as it will merely delete the entries from the MFT file while leaving the data structure of the files themselves intact.

The latter option is not quite as easy to dismiss: If you are still using Windows XP, the full format option basically functions like a quick format in disguise, with the addition of a quick scan for bad sectors on your hard drive (not recommended). In Windows Vista and Windows 7 however, choosing the full format will indeed overwrite your whole hard drive with zeroes, thus making a recovery impossible. Using this option is therefore a viable alternative to third party tools.

Also take a look at: How to install a Windows 8 upgrade on an empty hard drive

Deleting files from the iPhone and the iPad: Apple uses the file system HFC+ on both devices. In a nutshell, this means that files on Apple devices are handled quite similarly to files in Windows: Upon deletion, they are moved to a hidden folder called “Trash” and once this folder is emptied, all contained files are marked as deleted and discarded. Naturally, they are just as easily recovered from the abyss as they would be under Windows, so that this function should be used with caution.

Deleting files from Android: Up to version 2.2, Android makes us of the unconventional YAFFS system („Yet Another Flash File System“), which records all modifications to files in the form of a log (with the newest changes being added at the very bottom). This includes operations like renaming, moving and even deleting, in which case Android will leave a corresponding note at the end of said log without overwriting the actual data.

Luckily, all remaining file leftovers will eventually be wiped of your Smartphone's storage by Android's “Garbage Collector”. According to a study by the ETH Zürich, deleted files survive for an average 44 hours after being deleted (as long as the smartphone is in use), thus almost nullifying the risk of data recovery.

Every since version 2.3, Android uses the more conventional file system Ext4. This functions quite similarly to Windows and handles the deletion of files in almost the same manner.

Doing a factory reset: A great number of Notebooks, Smartphones and Tablets hide a factory reset function within their operating system. Sounds great – but what this function exactly entails differs from device to device. In some cases, your hard drive will be formatted and an out-of-the-box version of your OS reinstalled. Others might just reinstall a new version of your OS immediately without bothering to delete the old files. To be safe, either look up the exact scope of the factory reset of your respective device, or rely on specialized tools as described in step 2.

Read on page two of this guide how to delete files with specialized tools.

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