Kill Your Data

It's been more than a year since I wrote about how businesses have faced liability issues from data theft associated with incomplete disk erasure on discarded PCs and other devices (see "Dawn of the Undead Data," QuickLink 43381), and I still receive mail about it. The problem crops up

when the data you thought was completely erased isn't. In some cases, industrial spies, hackers or others can still access that information, which may contain company secrets or customer data.

Given rising concerns over privacy regulations and liability, it seems appropriate early in 2005 to clarify the issues and offer some practical advice.

Robert Houghton knows all about the liability issues surrounding disk erasure: He's president of Redemtech Inc., a company that reclaims computer equipment for businesses and must provide proof that data has been destroyed to its clients. If you're going to do it yourself, Houghton says to choose a utility that meets these five criteria:

  • It runs from a floppy or CD-ROM, independent of the resident operating system.
  • It's BIOS-independent -- that is, it can access the hard disk directly.
  • It's compatible with all drive hardware types and configurations in use.
  • It includes verification and error-checking procedures that can identify all failures.
  • It creates a report/audit trail proving successful erasure.

A good utility will overwrite all areas of the disk, including unallocated space and slack space -- areas where old data can reside unseen until someone with forensic tools inspects the medium.

Vince Tuesday, a security manager at a large financial services company, takes a pragmatic approach. "Any tool that can overwrite every sector with random zeros and ones with multiple passes should do the job," he says. Tuesday (not his real name) is a former columnist for Computerworld's Security Manager's Journal. He uses East-Tec Sanitizer, a disk-erasure utility from East Technologies. He runs the utility from a boot floppy and makes seven to 10 passes. At that point, he says, unless you're a government agency or university with huge resources to spend on extreme recovery measures, the data is pretty much unreadable.

Just what are those extreme measures? This gets back to the so-called residual magnetism issue I brought up in my previous column on this topic. It may be possible to recover overwritten data from the outer region of the tracks on which each sector of the original data was written. But Benjamin A. Carmitchel, president of ESS Data Recovery Inc., says most companies don't need to worry about that.

"While it is theoretically possible to recover data after it has been written over, practically speaking, it is not feasible unless the perpetrator spends about $250,000 for a spin stand and $80,000 a year for a knowledgeable engineer who can run the equipment and read the resonance data," he says.

Engineers at ESS have been able to use this method on mylar (floppy) media, but not on a hard disk drive -- yet. If foreign governments or the National Security Agency are interested in your data, you may have a problem. Otherwise, you can probably rest easy.

For corporate use, Carmitchel recommends X-Ways Security from X-Ways Software Technology AG.

"The fact that this program gives you an option to overwrite free and slack space up to nine times with random hex values makes it very reliable," Carmitchel says. While multiple erasure passes may help your peace of mind, he thinks one pass is adequate. The Department of Defense standard 5220.22-M, however, requires three. And other government guidelines for sanitizing media are classified and believed to be even more strict.

Ultimately, the easiest way to manage disk sanitizing for large numbers of machines is to outsource it. PC reclamation companies will erase the data for you as part of the disposal process. That's Tuesday's approach. His vendor uses Blancco Data Cleaner from Blancco Ltd., which wipes disks using a DOD-compliant algorithm. Inaccessible disks are destroyed, and Tuesday receives a certification of erasure and chain-of-custody documents for each asset.

Ultimately, however, IT must decide what level of disk sanitization is adequate, given the risks. In most cases, a multipass erasure process should be fine. But if the value of the data is high enough, the only fail-safe option is to melt or shred the disk.

Then again, all of this work will be for naught if employees have transferred sensitive data onto CD-ROMs or DVDs and then discarded them without shredding them first. Data recovery specialists have been able to recover data even from discs that were heavily scratched or snapped in two. But that's a subject best left for another column.

Robert L. Mitchell is Computerworld's senior features editor. Contact him at

Copyright © 2005 IDG Communications, Inc.

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