Securely Erasing a Drive for Selling

Throwing your old hard disk drive or solid-state drive out? Or perhaps you’re thinking about selling your computer or laptop? Make sure your data isn’t accessible to anyone else!

Many people wrongly assume that simply deleting the files off a hard disk drive or solid-state drive will render the data unrecoverable. But this couldn’t be further from the truth – anyone with access to free data recovery software can easily recover files from drives that haven’t been securely wiped. While formatting an HDD or SSD is certainly a better way of ensuring your data doesn’t fall into the wrong hands, it still doesn’t mean it can’t be recovered. Indeed, we’ve documented how to recover data from a formatted hard disk drive in the past. Reformatting a drive through Disk Management erases the address table, which contains the location of the data stored on the drive. When a file on a drive is deleted, the index file (or the “pointer” to the data) is deleted, but the actual binary data isn’t. The file system will recognise the file as deleted, and the space will be marked as free, ready to be overwritten with new data. But until new data is written to the sectors containing the deleted data, it will still be recoverable. If you want to ensure the hard drive or solid-state drive is usable (i.e. you’re ruling out physically destroying your drive), then you need to undertake a process known as sanitisation. Sanitisation goes beyond simply dragging files and folders to the Recycle Bin, and then emptying it, and goes further than formatting the drive.

Sanitisation is a non-destructive way of deleting data from a drive, and may be done for a variety of reasons. The most common is probably re-use, where you want a new user to be able to use your drive and not be able to access your old data. But you might also want to sanitise your drive if you are sending it in for repair, or are simply disposing of it – although physically destroying your drive is probably the best bet in the latter case. A great piece of free data wiping software we’d recommend is Darik’s Boot and Nuke, or DBAN. While it is no longer being updated, the free software can still be downloaded and used.

DBAN works by erasing every file on the drive and rewriting it with “pseudorandom” numbers, and needs to be run from a piece of removable media like a USB flash drive or CD/DVD. Once the software is burned to the bootable media, restart your machine, and if it isn’t automatically recognised, press F11 or F12, depending on the version of Windows you’re using. Once you’ve booted into DBAN, the interactive wizard will take you through the process from here. Once you’ve selected the drive you want to sanitise, the program will show you how far along the wiping is and how long is left. The user is presented with a green “pass” message once the process is complete.

Mac machines have a built-in method for sanitising hard drives, which can be found in the Disk Utility program. Power down your Mac, then power it up holding the command and R keys, waiting until the Apple logo appears. Select “Disk Utility” from the list of OS X Utilities, then “Continue”. Then, select the disk you want to erase, followed by “Security Options” – it is here where you can decide how thorough you want the wiping process to be. The most secure level of erasure within Disk Utility writes zeros across the disk seven times to ensure your data can’t be recovered.

Remember, if you truly want to make sure your data is unrecoverable, physical destruction is the best way – but sanitisation near guarantees the data is inaccessible forever.

Data Recovery