Computer owners are still disposing of storage and mobile devices full of recoverable data, according to a recent trawl of mobile devices, hard disk drives and solid state drives bought second hand from Amazon, eBay and by deletion and recovery specialists Blancco Technology and Kroll OnTrack.

Altogether, out of the 122 products acquired for the analysis in the UK, US and Germany, half of the storage devices and a third of mobiles contained residual data, including 2,153 emails and 10,838 text/SMS messages on the latter. Interestingly, of the storage drives found to hold data, for three quarters of them an ineffectual attempt had been made to delete data, with 61 percent being quick formatted, 14 percent reformatted, 11 simple file delete, 11 percent a random but incomplete overwrite and 3 percent by reinstalling software.

Image: Blancco

Clearly, then, the problem wasn’t that owners weren’t aware of the need to wipe storage before disposal and sale, more that they lacked the know-how or tools to do this. This is understandable. Wiping storage turns out to be more complex than it first appears and the tools chosen depend on what is being wiped and to what degree of certainty.

The process of permanently removing every trace of data from storage is termed ‘sanitisation’ and for business use is served by a small elite of expensive tools that will do the job to meet compliance and auditing standards. But what if the home or small business user wants something more occasional? Head on to the Internet and the user will encounter two dozen or more mostly freeware tools with varying capabilities and development histories.

Before using one of these it is important to understand some of the issues surrounding the task of sanitising a disk for re-use, re-sale, or disposal.

Best disk wiping tools - forget default commands

The first rule is not to rely on file deletion, quick formatting or re-formatting through an operating system such as Windows – all of these methods either don’t delete the file on the drive (simply the reference to it in the file allocation table) or can be reversed later with the right tool. Low-level formatting can securely wipe data but the effectiveness could still depend on the operating system used to carry out the action so it’s best not rely on it.

Best disk wiping tools - the tool depends on the task

Disk wiping is a non-destructive way of permanently removing data very different from data destruction, either physical or using a degaussing system that does the same job at the expense of destroying the drive itself.

There are a surprising number of high-quality tools (see end for selected suggestions), most offered as freeware or as limited versions of paid products.

Simple file or directory shredding can be done from within the OS as can the wiping of a partition. However, deleting an entire drive running an OS requires using a tool that can create boot media to do that from outside the environment, either on media or a USB stick.

Thinking laterally, it is also possible to fully encrypt data on a drive before deleting the key. The three issues with this – first deleted data on the surface of the drive won’t be encrypted unless full-disk encryption is being used and there is always the very remote chance that the encryption scheme will be cracked in the future. Third, it will potentially take a lot longer to use encryption than satisfactory data wiping.

Next - sanitisation standards

Best disk wiping tools - sanitisation standards

All wiping tools randomly overwrite storage but the method used to do this varies from tool to tool. One way is to use products that adopt a defined method while all will also usually allow the user to implement a random 1-pass approach.

Amidst a blizzard of standards, the baseline is probably the US Department of Defense’s DoD 5220.22-M (3 or 7-pass), but a selection of others including the Russian GOST R 50739-95 (2-pass), Schneier (7-pass), Gutmann (an extraordinary 35 passes) will also turn up on the spec sheet along with several others. Arguments abound about where the point of overkill kicks in but we can’t recommend one over another. All of the above will do the job on a technical level and originate in governments at some point in the last 10-15 years with occasional revisions.

Note: if the device is being used in a BYOD setting it is wise to check any policies on data retention first. The user will own the device but not necessarily the data.

Best disk wiping tools - proof of erasure

Products will normally offer the option of verification, at the expense of adding time, plus a log of some kind showing what the utility has done to the drive and its data. Anyone wiping a drive of any kind in a commercial organisation should hold on to this as proof that the data on it was wiped.

Best disk wiping tools - mobile devices

Mobile devices offer a particular challenge although there seem to be plenty of apps that claim they can do the job. Certainly, device reset functions should not be relied upon. The simplest method, where supported, is simply to encrypt the internal storage before initiating a factory reset. Some also suggest filling the phone with dummy data before repeating the process. As for removable microSD cards, the best option is to take them out of the device as use a PC utility to wipe them.

Best disk wiping tools - free tools

There is a plethora of freeware data wiping tools but it’s important to consider whether they will do the job asked of them – it might in some circumstances be worth paying for a utility. The biggest problem is simply finding one that can be relied upon from a field full of strong contenders.

We’ve chosen a selection of the better-known ones here to offer some direction. There are a lot more out there.

Best disk wiping tools - DBAN (Darik’s Boot and Nuke)

The small company that established this software, Geep, was bought out by Blancco 2012 but the utility lives on for anyone wanting to erase a hard drive as an open source project for home use only. Works by writing an ISO to a CD or USB stick, then used to boot into the utility. Supports six sanitisation standards including DoD 5220.2M, Gutmann and NIST 800-88 that offer a log but no certifiable erasure proof.

Pros: Has a good reputation for sanitising ATA, SATA and SCSI hard drives, easy to use

Cons: doesn’t support SSDs, no updates or support

Next: Disk Wipe

Best disk wiping tools - Disk Wipe

Unlike DBAN, Disk Wipe is a portable utility that works within Windows and can’t therefore be used to wipe the primary hard drive. It is, however, perfect for sanitising other drives, including USB sticks, external hard drives and memory cards. Supports DoD 5220-2.M and Gutmann and can also be used by commercial organisations.

Pros: Portable, good for sanitising external drives, can be used by anyone

Cons: Won’t work with primary drives

Best disk wiping tools - Secure Erase for SSDs

SSDs have a reputation for being difficult to erase thanks to the different way they operate at a low level compared to hard drives. One cited solution is to use something called Secure Erase (HDDErase) from the Center for Memory and Recording Research, executed the Secure Erase function built into Serial ATA (SATA) and Parallel ATA (PATA) hard drives. It’s a simple DOSlike utility that runs as a boot utility from media or a USB stick, basic but said to work.

Pro: Copes with SSDs

Con: Not exactly new – the utility is from 2008

Best disk wiping tools - Blancco 4

This will also wipe SSDs as well as hard drives and has a good reputation. Given the dearth of tools that can cope with this type of storage we’d strongly advise at least considering the single-PC license fee of around £18 ($25) for the capability it offers. The company also offers a wide range of enterprise products. Blancco 4 can be tried free of charge on evaluation.

Pro: a complete solution

Con: not freeware