HOW TO MAKE SURE INFORMATION ON YOUR OLD COMPUTER IS REALLY, TRULY DELETED / THE WALL STREET JOURNAL

How to Make Sure Information on Your Old Computer Is Really, Truly Deleted

It isn’t as simple as pressing ‘delete’ and emptying the Trash. Here’s a step-by-step guide.

By Sean Captain

Illustration: Jon Krause

Key Points

- Old computers hold sensitive data like tax returns and personal photos that can be recovered.

- Windows and macOS have features like “Reset this PC” and “Erase Assistant” to thoroughly wipe data.

- For older systems or nonfunctional computers, use KillDisk or physically destroy the hard drive.

Spring-cleaning season is almost done, and it is time to finally get rid of that old computer. 

But be very careful before you sell, give away or recycle it.

You could be handing over sensitive information.

Even if you think you deleted everything on it, your old computer may hold lots of personal items you don’t want anyone seeing. 

In a 2019 study by the University of Hertfordshire (funded by security tech-reviews site Comparitech), researchers purchased 200 used hard drives from the U.S. and U.K. 

An analysis found data remaining on 59% of the drives, including passport and driver’s license scans, bank statements, utility bills and “intimate photos.”

Just pressing “delete” and emptying the Trash in macOS or the Recycle Bin in Windows won’t do the trick. 

That’s because your computer maintains an index of where every file resides. 

Deleting a file erases only its entry in the index, telling your system that it can put new files in that space. 

But until the system actually does put new files there, the old ones remain accessible. 

Simple consumer-level file-recovery apps can get at it—never mind professional-grade forensic software.

Here’s how to make sure your data is really gone—even on a computer that won’t start up.

Back up and log out

Start by backing up anything you want to keep. 

You could drag files onto an external hard drive or use backup software such as the Time Machine app in macsOS. 

You can also back up to the cloud using Microsoft OneDrive, Apple iCloud, Google Drive, Dropbox or other services. 

(Don’t empty the Trash or Recycling bin. The wipe process will take care of this.)

Next, log out of applications or games with an online component, so the license is no longer associated with your old computer. 

Also do this for services like Gmail or Facebook, and web browsers like Chrome that sync your data online—on the admittedly remote chance that an incomplete wipe allows the next owner to access those accounts.

Another step for any type of computer is making sure your files are encrypted—scrambled in a mathematical operation based on very long strings of random numbers and letters called encryption keys. 

The wiping process will delete the keys to make sure any files that may remain on the machine are unreadable.

What you do next depends on your operating system.

Clearing out a PC

Windows 10 and the current Windows 11 have a feature called “Reset this PC,” which, with the right settings, thoroughly wipes your data. 

First, make sure your operating system is up-to-date, as Microsoft recently fixed a bug that sometimes caused the reset process to fail. 

Press the Windows key, search for “updates” and select “Check for updates.” 

Install any that are available.

Now check on encryption. 

In Windows 10 or 11 Home editions, press the Windows key and search for “device encryption settings.” 

Click “Device encryption settings” on the next screen, then make sure the switch next to “Device encryption” is toggled on. 

Windows Pro, Enterprise and Education editions have an encryption utility called BitLocker. 

To enable it, click the Start button, type “bitlocker” and select “Manage BitLocker” from the list of results. 

(All versions of Windows 10 and 11 also encrypt deleted files.)

Now you’re ready to wipe. 

Tap the Windows key again, search for “Reset this PC,” then click on it. 

On the next screen, tap “Reset PC” (Windows 11) or “Get started” (Windows 10), and on the following screen, click “Remove everything.” 

On the next screen, select “Local reinstall.” 

(If this doesn’t work, try the “Cloud download” option.) Then click “Change settings,” and on the following screen (under “Clean data?”), toggle the switch to “Yes” and press “Confirm.” 

On the following screen, press “Next” (Windows 11) or “Reset” (Windows 10). 

On Windows 11, you will press “Reset” on one more screen. 

Then let the process run for a few hours.

“Reset this PC” deletes your files, apps and settings, logs you out of your Microsoft account and disables the “Find My Device” feature so the computer is no longer associated with you. 

Then the serious wiping starts. 

The encryption keys are deleted, making any encrypted data irretrievably scrambled, and the Clean data option overwrites the ones and zeros that had encoded data on your drive. 

A clean copy of Windows is also installed.

The MacOS method

Apple’s “Erase Assistant” feature made its debut in 2021’s macOS 12 Monterey. If your current OS is older, you may be able to update it. 

To update an older OS to Monterey or a later one, click the Apple menu, then “System Preferences” and “Software Update.” 

If the update process doesn’t work, jump to “If all else fails” below for another option.

As with Windows, the “Erase All Content & Settings” process should start with encryption. 

On newer Macs (starting between 2018 and 2020, depending on the model), data is encrypted automatically. 

Just to be safe, though, turn on a feature called FileVault that adds encryption to older systems and an extra layer to newer ones. 

Click the Apple icon, then “System Settings” (or “System Preferences” in Monterey). 

In the next window, click “Privacy & Security” (or “Security & Privacy”), then click FileVault.

Now it is time to wipe. 

Click again on the Apple icon and “System Settings” (or “System Preferences”), click “General” on the left, then “Transfer or Reset” on the bottom right. Finally, on the next screen, click “Erase All Content & Settings.” 

(In Monterey, you’ll go there directly from “System Preferences.”) 

This process signs you out of Apple services, turns off the “Find My” and “Activation Lock” security measures so that the system is no longer associated with you, and erases all your files, settings, apps and anything else. 

It deletes the encryption keys, permanently scrambling any data that remains.

If all else fails

If your PC or Mac is so old that it can’t run a modern wipe process, you have one more option before seeking pro help. 

For Windows, several experts recommended the KillDisk app. 

The $49.95 Professional version runs from a USB drive and overwrites the ones and zeros that encode data on your hard drive with all zeros. 

Afterward, your computer will no longer boot into Windows unless you reinstall the OS.

For a Mac, your best option is a complex process that Apple describes online.

If these processes sound too complicated, or if your system won’t even turn on, use Apple’s recycling program for Macs or a disposal company that offers hard-drive destruction (or shredding) and recycling for consumers with either type of system. 

Look for ones that issue a certificate of destruction to verify the process. 

For instance, Ship ‘N’ Shred accepts drives or whole devices, with prices that include shipping ranging from around $30 to $200.

Modern technology leaves a lot of digital footprints, but at least you can sweep them off your old computer.

Sean Captain is a writer in New York.