How do you securely erase files from your hard disk? Once you delete a file, drag it into recycle or trash and then empty that bin it’s gone, right? Wrong. If you are considering selling a Desktop or Laptop you need to securely wipe it first. Ask this guy.

The header of the file is overwritten, not the file. Basically the file loses its ‘I’m here’ flag on the disk.

OS X has a built in secure erase trash option, it writes over your deleted files with random data seven times, meeting the now aging US Department of Defence guidelines. Please note that after this very few – in fact none that I know of – commercial products can get data back. Specialists and the military organisations will be able to though. If you want to delete data to the point that nothing can get it then it needs to be overwritten 32 times. That defeats even an electron microscope.

No Windows OS offers this solution so you need a third party tool on Windows. Tune Up utilities offers this as does Norton Utilities. But I’d rather feed my hard disk to a Bug-blatter Beast of Traal than install anything by Norton. A free tool is the nice Blowfish Advanced CS 2.57. Linux also has a number of tools like Wipe.

What about the whole disk? For example if you are selling a Desktop or Laptop you want to make the disk unrecoverable – well I do anyway *tin hat*.

That option is built into OS X again, throw in your Tiger disk, reboot holding C, use Disk Utitlity before you go any further into the install routine. Select the Erase tab, Click on the Options button. This gives you standard erase which offers no security, 7-pass which is the old military standard and 35-pass which means nothing is getting data back. A word of warning though the latter option takes forever to complete, if you do this your disk will be grinding away for 14-24 hours or more depending on the disk size. A lot of third party tools offer this but it is on the Apple disk so why spend money? Though you need to spend money to recover files.

For Windows we’re back to third party tools, Windows is not built for security so we have to use other programs that OS X just has by default. I’m hoping that Vista will have these options. Some tools that are for windows are Paragon Disk Eraser and WipeDrive.

The easiest solution to a full disk wipe on any x86 computer – and Apple Mac PPCs – is a free boot floppy/CD called DBAN. This quickly and securly erases your disk and all you have to do is boot up your computer. Label this disk in BIG letters, one not to use by mistake.

Another solution is to buy a degausser, though this is really an expensive solution for wiping a lot of disks. Basically a huge electro-magnet that wipes the disk clean in 60 seconds. Fast but expensive. Also remember Fujitsu’s caveat, your disk will still be readable by experts after this.

… enabling security-conscious firms to permanently remove data from hard drives, backup tapes, floppy disks, and the like. Plus, since Fujitsu only promises protection against commercial recovery methods, its probably still best to destroy drives used for illegal activities the old-fashioned way, by tossing them into a wood chipper.

Link.

For those on OS X who want to delve deeper into security get Apple’s Common Criteria Tool. A long list of tools is here.

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