There is justifiable concern about data security when it comes to both disposing of and re-using hard drives and so the purpose of this brief article is to give some ideas regarding how to wipe a hard drive. This is emphatically not paranoia; however some of the theories surrounding what is required to securely remove your sensitive data from a drive stray into this area.
First of all it is worthwhile clearing up a few fallacies. When you delete a file, it has not been erased. The entry referring to the file in the hard drive’s “index” is marked to indicate that the physical space occupied by that file is now free to be used for another file, however until a second file overwrites the original data then it is still extant on the drive (and easily recoverable). Due to the way that free space is used by your operating system it is difficult to say when (or if) the space occupied by your deleted file will be overwritten, therefore it is always wise to assume that a deleted file still exists on your hard drive.
Secondly, if you re-format your drive, this too does not guarantee that the files that existed previously have been removed. A simple re-format will in fact almost certainly leave the vast majority of your data still in existence on the hard drive (albeit rather more difficult to locate and recover than would be the case if a file were to be simply deleted).
For these reasons it is therefore important to understand how to wipe a hard drive. Note however that if you are not planning to re-use the drive then destruction may be a more simple option. In this case you need to remove and destroy the platters inside the drive chassis in order to ensure that your data is beyond recovery. Access to the drive will typically require Torx screwdrivers, however the determined application of a hammer and chisel will get you there without them. Once you have retrieved the platters you can either shatter or bend them (see the picture below), which is appropriate will depend upon the material used to make the platter, either will ensure that access will never be possible again. Where shattering is appropriate it is best to put the platters into a bag before breaking them as you will find that the pieces fly everywhere.
How to Wipe a Hard Drive:
The first thing to bear in mind is that in order to do this correctly it is necessary to overwrite every sector on the drive. This will take time, exactly how much time will of course depend upon the particular method used and the hardware arrangement in place, however it will be hours rather than minutes. If a “wiping” technique only lasts for a few minutes then it has not done the job. In broad terms expect a drive of 500GB capacity to take an absolute minimum of a couple of hours (and in all likelihood 5 hours or more) in order to be completely wiped.
There are numerous free utilities which provide a satisfactory solution to how to wipe your hard drive. They all do much the same thing and so the choice will be down to individual preference and the operating system that you are using.
If the hard drive which you intend to zero-wipe is the one from which you usually boot your computer then perhaps the simplest way of safely and effectively wiping a disk is to download a bootable CD from the hard drive manufacturer, all of the major hard drive manufacturers provide this facility in one form or another:
Seagate (which also includes Maxtor and Samsung drives):
Western Digital (look for Data Lifeguard Diagnostic for Windows)
Hitachi (includes IBM):
Each of these offers a CD image file which can be used to create a bootable CD.
If the drive to be wiped is not your boot drive then you will need to boot from a second drive with the drive to be wiped connected as a slave (if your computer uses the older style IDE ribbon connector cable to its hard drives). If your computer uses S-ATA connectors then you should be able either to connect the drive to be wiped alongside your boot drive directly to a spare S-ATA cable or alternatively you could use an external caddy and connect it to a USB port on your computer.
You can download utilities specifically intended for the purpose of securely wiping a hard drive. An example is Killdisk which offers a freeware program compatible with pretty much any variety of Windows.
With all methods of hard drive wiping, take great care not to erase the wrong drive, once these processes have completed then there is no data left to recover (that is after all the point). Always remember the golden rule, to over-write the data on your hard drive will take hours not minutes, whichever method you choose if the wiping procedure only last for a few minutes then it has not done the job.
There is much talk about how many “passes” are required in order to be sure that the data has been overwritten and cannot be recovered. In other words how many times does each sector have to be over-written in order to be sure that the previous data has gone? The short answer to this is once. There is some debate about the very early models of hard drives potentially retaining some of the previous data signals following an over-write but no one has ever credibly demonstrated that they could recover meaningful data from a sector that has been overwritten once on a hard drive made in the last 10-15 years. By all means if it helps you to sleep better at night run the drive wiping procedure as many times as you wish, but the first time will do the job.
In summary, if you have no intention of re-using the hard drive then platter destruction is probably the easiest route to ensure that your data will never be compromised. If the drive is to be re-used then there are any number of effective ways of over-writing every sector on the drive and therefore expunging your data. Knowing how to wipe a hard drive is not paranoid it is an essential part of protecting yourself.
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