Computers are increasingly used to store confidential information such as personal, financial or medical records. This information is magnetically stored on the computer's hard drive, and should be completely removed before discarding, recycling or selling the hard drive. Erasing, formatting or even overwriting the drive are not sufficient to guarantee removal of the stored information. Files that have been deleted and overwritten can be recovered with special hardware and software. Common commercial software packages are relatively quick and simple to use, and will discourage all but the most sophisticated data thieves. More thorough methods are available, but are considerably slower. If you believe the data to be of exceptional value, consider using a Guttman algorithm procedure. The National Security Agency (NSA) and other organizations opt for physical destruction for maximum security.
Purchase a software package that is compliant with Department of Defense Standard 5220 (DoD 5220.22-M), which is the U.S. standard. This standard specifies a three-pass scrub, writing the entire disk with "1," "0" and random data.
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Install the software on the computer where the hard disk is located.
Follow the manufacturer's instructions to run the software and verify that it has completed the scrub task. For large-capacity drives, this can take several hours. When the software is complete, your disk is now scrubbed. It will be unreadable to all but the most sophisticated computer forensics professionals.
Procure a software package that uses the Gutmann algorithm, either from a retailer or online. This method of software scrubbing completes 35 write cycles of the entire hard disk.
Install the software on your computer.
Run the software on the desired hard drive per the manufacturer's instructions. This method scrubs the disk in a manner that is not recoverable by any known method. However, it will require days to weeks to run on large hard drives.
Open the computer case and remove the hard drive. It will usually be held be several screws and have one or more cables attached to it.
Drill several large-diameter holes (greater than 1 inch) completely through the center of the drive.
Recycle or discard the drive, as appropriate.
Things You'll Need
Data removal software
Power drill with one inch bit (optional)
Deleting a file on a hard disk does not physically delete the file, but simply allocates the space as being available for re-use. The information is still present. Formatting a drive may make the files unavailable to a computer operating system, but again the data is still present and can be recovered. One-pass overwriting the drive will not scrub the data, as is possible to discern the previous value of a magnetic storage bit through careful analysis.