Deleting files from a hard drive does not remove them completely from the computer. The operating system removes the reference to the file in the file allocation table, but the data remains. This data is not completely removed until the hard drive stores other data in the same location, overwriting the previous data. Hard drives should be fully erased (data wiped) to prevent the possibility of recovery using specialized software. After the data on the hard drive has been completely erased, the hard drive can be destroyed or recycled.
Data wiping, also known as secure erase, is a procedure performed to permanently delete data from a hard drive. Data wiping is often performed on hard drives containing sensitive data such as financial information. It is not enough to delete files or even format the drive. Software tools can still be used to recover folders, files, and even entire partitions if they are not erased properly. Use software specifically designed to overwrite data multiple times, rendering the data unusable. It is important to remember that data wiping is irreversible, and the data can never be recovered.
Secure erase software takes a long time to erase a disk. Many programs offer multiple choices for overwriting data. Special patterns of 1s and 0s, mathematical algorithms, random bits, and multiple overwrites can be used. With disk sizes reaching in excess of 2 terabytes, along with multiple overwrites, it might not be practical to use data wiping software, especially if you have many disks to wipe. Because data is stored magnetically on a hard drive, magnets can be used to erase them.
Degaussing disrupts or eliminates the magnetic field on a hard drive that allow for the storage of data. An electromagnet is a magnet, that when a current is applied, its magnetic field becomes very strong. A degaussing tool can cost US$20,000 or more, so it is not a practical solution for most users. It takes about 10 seconds to degauss a hard drive, so it can save a lot of time and money if a large number of hard drives need to be securely erased.
There are also degaussing wands that can be used for smaller jobs, as shown in Figure 1. A degaussing wand uses powerful magnets instead of electromagnets and costs much less. To use a degaussing wand, a hard drive must be disassembled and the platters exposed to the wand for approximately 2 minutes.
Hard Drive Destruction
Companies with sensitive data should always establish clear policies for hard drive disposal. It is important to be aware that formatting and reinstalling an operating system on a computer does not ensure that information cannot be recovered. Destroying the hard drive is the best option for companies with sensitive data. Drilling holes through a drive’s platters, as shown in Figure 2, is not the most effective method of hard drive destruction. Data can still be recovered using advanced data forensic software. To fully ensure that data cannot be recovered from a hard drive, carefully shatter the platters with a hammer and safely dispose of the pieces.
Solid State Drives
SSDs are comprised of flash memory instead of magnetic platters. Common techniques used for erasing data such as degaussing, and shattering are not effective. To fully ensure that data cannot be recovered from an SSD, perform a secure wipe or shred the drive into tiny pieces.
Other storage media, such as optical and floppy disks, must also be destroyed. Use a shredding machine that is designed to destroy this type of media.
Hard Drive Recycling
Hard drives that do not contain sensitive data should be reused in other computers. The drive can be reformatted, and a new operating system can be installed. Two types of formatting can be performed:
- Standard format - Also called high-level formatting, a boot sector is created and a file system is set up on the disk. A standard format can only be performed after a low-level format has been completed.
- Low-level format - The surface of the disk is marked with sector markers to indicate where data will be stored physically on the disk, and tracks are created. Low-level formatting is most often performed at the factory after the hard drive is built.