What do you do with your old hard disks, flash memory, and solid-state drives when you’re no longer using them? Perhaps you upgraded from a 1GB flash drive to brand new 32GB stick and you just thought you’d delete everything on your old device to give to a friend. What did you really just give them though?

You might already know that simply deleting files in the Finder or Windows Explorer & emptying the bin is insufficient to securely erase data, so how do you wipe storage media clean? Re-formatting? Not enough!

The only secure method to destroy sensitive data – while maintaining the ability to re-use the device in question – is to overwrite it with new data, random or otherwise. Multiple times, too – if you’re using magnetic storage, which unfortunately adds time to completion. Flash & solid state mediums have the distinct advantage of being immune to magnetic fields, so a single overwrite is perfectly secure; in fact running multiple unnecessary wipes can shorten the lifespan of your flash or SSD device.

Lucky for you there are several ways to securely erase free space, a single partition, or an entire device. Let’s take a look at some of the choices:

DBAN (Darik’s Boot And Nuke)

DBAN (free & open source) runs on any PC with a standard BIOS, regardless of what operating system is installed. Downloading DBAN takes just a minute, and gives you an ISO image that you can burn to a CD or DVD. Once you have a DBAN disc ready, restart your computer and set your BIOS to boot from the optical drive first. Once booted to DBAN, you’ll see instructions for how to quickly start erasing all hard drives in the computer (be careful!), or you can just press return to boot a friendly interactive mode that lets you specify which partition(s) or whole drive(s) in your computer to erase, what technical method of “randomness” you prefer, and how many times you want to overwrite the device. Support for RAID controllers & external devices is minimal to non-existent, but you’ll be happy to know if your PC has a floppy drive DBAN can save a log of its actions to a diskette for your review.

Mac OS X Disk Utility

Disk Utility (included with OS) provides an easy way to securely overwrite data in all versions since Mac OS X Panther. There’s nothing to download or install, and you don’t even need to restart — unless of course you want to erase the active boot volume. Found in Applications > Utilities, Disk Utility gives you the ability to wipe any volume(s) or drive(s) as many as 37 times, or even just wipe the free space on a volume without destroying the entire partition. The best thing Disk Utility has going for it besides ease-of-use is great compatibility: if Mac OS X can see and use it, Disk Utility will erase it!

Eraser

Eraser (free & open source) is an application you install, based on the same technology as DBAN, that brings some of Mac OS X Disk Utility’s features to Windows. Specifically, it allows you to securely erase just the recycle bin’s contents (similar to Finder’s Secure Empty Trash option), erase just the free space on a partition, or overwrite an entire partition’s contents. As with Disk Utility, it also just works with any drive Windows can see, breaking through the limitation of DBAN’s live boot with its basic driver set.

dd

dd (free & open source) is a command built-in to most Linux and UNIX distributions that also shares the advantage of being able to work with any drivers currently loaded in the host OS. A simple command to erase a whole drive would be:

dd if=/dev/urandom of=/dev/sdb bs=1M

Where sdb is the device you want to erase. Unfortunately dd has no indication of progress & time remaining as with all of the alternatives.

Active@ KillDisk

KillDisk (free edition, Pro from $39.95+), at first glance, appears to be the hybrid offspring of DBAN + Eraser, though it pre-dates both, and runs in DOS instead of Linux. The free edition will let you write zeros over any partition (or whole drive), but if you want to overwrite with random data you’ll have to cough up $39.95 for the Pro version that runs in DOS only (the Windows version starts at $49.95). The DOS version is not compatible with as many devices as DBAN, and the most useful “Pro” functionality in the Windows version comes free with competitors, so for these reasons we recommend checking out the alternatives first.

Magnets Don’t Work

The #1 myth about data destruction is that a powerful magnet will erase & protect your data. The truth is that no magnet you can take home will do this for you, otherwise the bone-crushing magnet that’s already in your hard drive would be erasing data for you! In the December 4, 2008 episode of Security Now, host and security & hard drive expert, Steve Gibson, explains that simply trying to degauss a hard drive with a magnet from the shell produces no results, and that the simplest & best method to prevent data recovery from a decommissioned storage device is to physically destroy it.

Hammer Time

If you have no use for a disk drive anymore, or have a defective device, the best method for secure data destruction is to physically destroy the device beyond repair. Check with your toolbox, garage workshop, or local home improvement store for ideas and assistance. There are companies and organizations that will shred storage media for you, but these are typically only available to businesses with large amounts of equipment to crush and recycle.

1-800-HOSTING employs several methods of secure data erasure and destruction, including all of the methods described above. Does your hosting company have your security (and your customer’s) in mind?