How to Really Delete Data for Absolutely Sure

Everyone knows by now that when you delete data on a computer, it's not necessarily completely gone. The importance of this fact, and the need to be able to delete data with absolute certainty, has increased in recent years.

Imagine that you are upgrading, or taking out of service, a server that has had confidential data stored on it. This could be patient records in a hospital, credit card data in a retail organization, secret weapon plans in a defense plant, whatever. What do you do with the hard disks in the server? There are serious compliance issues at stake here.

Hard disks these days don't have much of a lifetime. The disks from a server you built two or three years ago are probably not worth saving for another use. But you can't just throw them out.

Standard formatting tools aren't perfect. They're not designed to eliminate data completely, but more to get the disk blank enough and set up for new use. In fact, all software tools have a tough job eliminating data, in that old data can survive multiple writes. Nevertheless, there are software products (such as those from Blancco) that erase data to varying standards of completion.

I have had to throw out a few personal drives over the last few years, generally when installing larger ones, and I've taken the old-fashioned approach to data destruction. I put the drive on the floor of my basement, and I give it a few whacks with a hammer. After that, the drive maybe useful as a maraca, but I challenge anyone to get meaningful data out of it. This method should be fine on drives made with glass platters, but some, alas, are made with aluminum.

There are many other forms of physical destruction to which you can subject your drives to make the data unrecoverable. You could drop them in an active volcano, for instance. This isn't convenient for most enterprises, and I haven't located any services in this area. Last year we saw the emergence of a new device: the hard disk shredder, which can chop an entire drive up into metal and glass and plastic confetti. This should do the job, but these devices are rare and expensive. They also create trash that is difficult, if at all possible, to recycle.

All of this is why the NSA defines rules for how to "sanitize" devices of data. They call for degaussing, which means to eliminate the magnetic fields in the device. Since the data exists on hard drives in the form of magnetic fields, this amounts to deleting the data.

You can buy commercial degaussers, such as those from Fujitsu. The new Fujitsu Mag EraSURE ME-P3 degausses magnetic media, including VHS tapes, in as little as 15 seconds. You can then safely send the drive out to recycling; a hard drive, however, will not function after degaussing, so you have to trash it somehow.

What's really interesting about these devices is the potential for an outsource market to develop. Degaussers like this are cheaper than shredders, but they still cost a lot (the high-end Fujitsu Mag EraSURE ME-P3 will sell for $53,000), so many companies who might need to use one can't justify the cost. What if companies put them on a truck and drove out to locations, like those paper shredding services, to degauss your drives? They could provide a certification, even video evidence, that the drive was erased, and maybe then even take it away for proper disposal.

One-man shops like me can make do with a hammer, but large businesses need something more sophisticated. Degaussers could be the ultimate tool.

Security Center Editor Larry Seltzer has worked in and written about the computer industry since 1983.

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