Completely wiping a computer ensures no data can be recovered from the hard drive. This is important when donating, selling or disposing of a computer. It also allows you to do a clean install of an operating system.
Why wipe a computer?
There are a few key reasons to wipe a computer:
- Remove personal and sensitive data before selling or donating the computer
- Eliminate malware and viruses that may be hiding in the hard drive
- Reset the computer to factory settings before performing a clean install of an OS
- Comply with data protection regulations if the computer contains customer data
Failing to fully wipe a computer puts confidential information at risk. Things like financial records, business documents and login credentials could be recovered by someone else.
How to wipe a computer hard drive
These are the main methods to securely erase data from a hard drive:
Use disk utility software
Disk utility tools built into operating systems or available as third party software can wipe entire hard drives. Examples include:
- Windows – Diskpart erase command
- macOS – Disk Utility
- Linux – shred command
- Darik’s Boot and Nuke (DBAN)
- KillDisk
- Eraser
These tools overwrite all hard drive data with zeros or random characters. This renders the original data unrecoverable.
Physically destroy the hard drive
For maximum data security, physical destruction is an option. This could involve:
- Using a hammer to damage the platters and mechanism
- Drilling holes through the hard drive
- Running a strong magnet over the drive to corrupt data
- Crushing or shredding the entire hard drive
Physical destruction is time consuming and permanently disables the hard drive. But it provides absolute assurance that no data can ever be recovered.
Use manufacturer secure erase commands
Some hard drive manufacturers support a secure erase command built into their firmware. For example:
- ATA secure erase – supported by most hard drives
- Apple Secure Erase – For erasing Apple SSDs
- HP Sanitize command – For HP enterprise hard drives
These commands perform a cryptographic erase procedure at the hardware level. They provide assurance of data erasure equal to physical destruction, while allowing drive reuse.
How many overwrites are needed to wipe a hard drive?
There is debate over how many rewrites are required to fully erase a hard drive. Standards range from just one pass to overwriting 35 times.
overwrite all data once sufficient to wipe most hard drives. Intelligence agencies tend to recommend at least three passes to guarantee data erasure. The more wipes, the lower the chance of any data reconstruction.
Overwrite standards include:
- DOD 5220.22-M – 3 pass wipe
- NIST 800-88 Rev 1 – 1 pass
- Gutmann method – 35 pass wipe
- Bruce Schneier method – 7 pass wipe
While multiple overwrites are generally recommended, a single wipe pass through hardware encryption or block erasure can securely erase data on modern drives.
How to wipe a hard drive before selling a computer
When selling or donating a computer, you should wipe the hard drive to protect your personal data. Follow these steps:
- Backup any important data on the computer
- Reset the computer to factory settings if possible. This will remove files and wipe confidential data from the OS.
- Use disk utility software to overwrite the hard drive (see recommendations above)
- If the computer has an SSD, use manufacturer secure erase tools like Apple’s Secure Erase
- Reinstall the OS to test the wiped hard drive
- Remove any confidential stickers, labels or tags from the computer
Following this process will sanitize the hard drive and restore the computer to an out-of-box state before selling it.
How to wipe a hard drive before donating a computer
Donating old computers to charity is a nice gesture. But you need to protect your data first. Follow these tips:
- Backup important data off the computer
- Research the donation organization’s wipe policies. Some may wipe drives for you.
- Use disk utility software to perform a multi-pass wipe of the hard drive
- Physically remove and destroy the hard drive if you are not comfortable with software wipes
- Install a fresh OS to test the wiped hard drive
- Delete all personal files and accounts from the PC before donation
Donating a fully wiped computer avoids your data falling into the wrong hands. Safely sanitize the hard drive first before passing it on.
How to wipe a laptop hard drive
Laptops have the same data security issues as desktop PCs. Follow these steps to fully wipe a laptop hard drive:
- Back up any data you need to keep
- Check the laptop manufacturer’s website for a secure erase utility tool.
- If no tool is available, use a platform independent wipe utility like DBAN.
- Boot the laptop from the DBAN CD/USB and select the wipe option.
- Use a multi-pass overwriting method to wipe the hard drive.
- Reinstall the laptop’s OS after wiping completes.
Wiping a laptop hard drive this way will completely erase its data for security when disposing of the system.
How to wipe an SSD hard drive
Solid state drives (SSDs) store data differently than mechanical hard disk drives (HDDs). This requires specialized wipe techniques:
- Use the SSD maker’s secure erase tool if available. For example, Samsung Magician and Apple Secure Erase.
- Set the SSD controller to encryption mode before performing a standard wipe. The encryption key will be erased making data inaccessible.
- Wipe SSD free space to sanitize deleted files. Tools like Parted Magic can do this.
- Perform multiple overwrite passes for maximum data destruction. Or physically destroy the SSD.
Take care when wiping SSDs. Trim commands and wear leveling can allow data recovery if not handled properly.
Can wiped data be recovered?
With the right forensic tools, it is sometimes possible to recover wiped data. However, there are several factors at play:
- The more wipes performed, the lower the chances of data reconstruction.
- SSDs store data differently than traditional hard drives, making data recovery difficult.
- Specialized techniques like degaussing and physical destruction render data unrecoverable.
- The cost of forensic data recovery is very high, often not worth the effort.
While there are never guarantees, multipass wiping of a hard drive makes meaningful data recovery essentially impossible in most cases.
Can deleted files be recovered from a wiped hard drive?
If a hard drive wipe has been performed correctly, deleted files cannot be recovered. Here is why:
- A full drive wipe overwrites all data – both existing files and deleted files.
- Wiping scrubs the free space where deleted files reside.
- File systems are reset, destroying references to deleted files.
- Drive reformatting after wiping creates new blank file system.
The only exception is data that may persist in “bad” sectors inaccessible to the wiping process. But this data is fragmented and meaningless.
Will wiped files be restored after reinstalling the OS?
After wiping a hard drive and reinstalling the operating system, the wiped files will not come back.
A full wipe overwrites all drive data with zeros or random data. The original files are overwritten and permanently deleted.
Reinstalling an OS creates a brand new blank file system. The OS starts from scratch with none of the original user data.
So a full drive wipe provides a clean slate before reinstalling OS files and applications.
Conclusion
Wiping a hard drive removes all data including the operating system, programs, and user files. The wipe process overwrites the drive sectors where data resides.
To maximize security, use multiple overwrite passes along with drive encryption tools. Or use physical destruction methods like crushing for permanent data sanitization.
Take time to securely wipe any computer before disposing of it. This will protect sensitive information that may otherwise be recovered.