Introduction

At some point, you may need to part with your computer. Whether it’s a company-owned machine that needs to be returned, or you’re selling it to upgrade to a new model, one thing is certain: it contains a lot of your personal data. Some of that data is likely quite sensitive.

Imagine if someone gained access to your photos, addresses, documents, passwords, or financial information. The potential consequences are alarming: identity theft, unauthorised purchases, fraudulent loans, ransomware attacks, or even blackmail. These scenarios sound frightening, but how real is the risk? Let’s break it down and explore how you can safeguard your data before letting go of your computer.

Understanding the Data on Your Computer

Sensitive Documents, Photos, and More

Chances are, you’ve saved various sensitive files on your computer over time; scanned passports, bank statements, or even pictures of your debit card. Most of these files should be easy to locate in your Home folder. However, files can be saved almost anywhere on your computer, so it’s essential to remember where you’ve stored them, especially when moving or downloading files.

Passwords and Logins

Hopefully, you’re using a password manager rather than saving your passwords in a plain text file like passwords.txt on your desktop. Password managers encrypt your credentials, providing a layer of security. However, if you do store passwords in a file, you’ll need to take extra precautions. Read more on protecting your data here.

Emails

If you use an email client like Thunderbird or Outlook, your emails are stored locally on your computer. Conversely, if you access your emails through a web browser (like Gmail), your emails are not typically stored on your device.

Internet Browsing History

Every time you browse the web, your browser creates a local copy of the pages you visit (including all the images that were loaded), known as a cache. This cache speeds up page loading times but also keeps a record of your browsing history, stored in a hidden folder. Anyone who knows where to look can easily find it. To discover where it is you can simply search Google for the location, e.g. Chrome cache location or Microsoft Edge cache location.

How Could Someone Access Your Data?

The ease with which someone could access your data depends on how thoroughly you’ve removed it. If you haven’t taken any steps to delete your files, they’ll be easy to find, even without the password to your account. Anyone can remove the hard drive, plug it into another computer, and browse your entire file system password-free (unless your account is encrypted).

What if You Delete All Files, Clear Your Browser Cache, and Set Up a New User Account?

This is better than doing nothing, but it’s not foolproof. When you delete a file or user account, the data isn’t actually erased. Instead, the space it occupied is marked as “empty,” ready to be overwritten when needed. Until it’s overwritten, the original data remains on the drive.

Programs designed to scan “empty” sectors can easily recover these files, often at little to no cost.

What if You Erase the Drive or Reinstall the Operating System?

Even if you erase the drive or reinstall the operating system, the same principle applies; the disk is simply lablled as “empty,” but the data isn’t immediately removed. Installing a new OS might overwrite some of the old data, but considering that a typical operating system is only about 25GB on a 1TB hard drive, most of your old files will remain intact.

How to Ensure Your Data Is Truly Gone

Option 1: Remove the Drive

The most reliable way to protect your data is to remove the drive from your computer before passing it on.

Replacing a drive is simple:

1. Identify the Drive Type: Turn off your computer, open it up, and check if you have a 2.5" drive (common in laptops), a 3.5" drive (desktop hard drives), or a more modern NVMe drive. Apple computers may have proprietary drives, so check visually.

2. Order a Replacement: Once you know the type of drive, purchase a replacement.

3. Prepare a USB Installer: While waiting for your replacement drive, create a USB installer for your operating system. For Windows, download the Windows Media Creation Tool. For Mac, follow these instructions. For Linux, use Rufus to create an installer from your chosen Linux distribution’s ISO file.

2. Zero Write the Drive: Format the disk by writing zeros over each sector. For maximum security, do this at least three times. This can be done from the command prompt using these instructions or with various free or paid software you can find from Google.

Zero write wiping corrupts any remaining files, making data recovery extremely difficult and expensive—unlikely for someone to attempt unless you’re a high-value target with major secrets.

Is There Anything Else?

There’s still a slim chance that someone could recover data from your computer’s RAM. RAM is a form of temporary storage that your computer uses to quickly access data needed for active tasks. For instance, when you’re working on a file in an application, that file is likely loaded into RAM for faster access. However, recovering data from RAM is far less common and requires significantly more effort and technical expertise.

If you can’t remove or zero-write your drive, your best bet is to delete all files, reinstall the operating system several times, and securely erase the free space. While this isn’t as foolproof as the other methods, it scrambles old data enough to make recovery challenging.

Ultimately, the safest approach is to remove and replace your disk. For about £30, you can enjoy complete peace of mind, knowing that your data won’t fall into the wrong hands.