This might come as news to some tech bros, but not everyone wants the files and data on their devices lingering around forever. Even if you think you've deleted something, there's a chance that data can be restored by someone determined, so it's important to properly delete and make sure that data you never want to see again is gone for good.
Selling or Recycling Your Device
You don’t want a new owner exhuming your data when you’re selling or gifting your old device, so to make sure everything is scrubbed, you need to do what's referred to as a Factory Reset. It'll delete everything, sign you out of all cloud services and put the device back to how it came from the factory. Here's instructions on how to do that for various devices:
When re-installing Windows, make sure to select the “Data Erasure” option when prompted. This does a "Secure Erase" and overwrites the data on the disk with gibberish, making it virtually impossible for someone to try and restore the data later. It takes a long time – sometimes many hours – but it's worth the wait if you're giving the device to someone else. Android and iOS devices do this automatically due to their encrypted by default nature. macOS will do a Secure Erase for Macs with Apple Silicon CPUs, but for Intel-based Macs you need to use Disk Utility in Recovery Mode as outlined in this document. If you’re unsure what type of Mac you’ve got, Apple has a handy document explaining how to find out.
While it's far beyond the average nerd's ability to restore data from a securely wiped device, it's not impossible for someone who is really determined and has the right expensive and restricted tools.
To be really sure no data can ever be restored, physically destroying the storage portion of the device yourself is the way to go. Make sure to crack and smash the flash memory portion (black rectangles the size of a postage stamp) – my personal technique is a power drill and some safety goggles.
You also need to take these steps if you're recycling the device as most of the time the device isn't destroyed, but cleaned up and sold to someone else or stripped for parts. Even if the device doesn't turn on, the storage can still be taken out, connected to another computer and retrieved that way!
Covering Your Tracks
What if you're keeping a device but just want to remove traces of your activity?
For files, the obvious first step is to empty the Trash/Recycle Bin on your computer. Simply deleting the file in Finder/Explorer isn't enough. You also need to go through any backups you might have (e.g: Time Machine on macOS) and delete the files from there too.
On Mac/Windows, you might also want to look into making a separate account for another user, or a "guest" account if you regularly have other people using your computer. When someone else wants to use the computer, they can log into their own account, or the guest account, leaving your stuff alone.
All web browsers have a feature to clear history, caches and cookies. Here's how to do that:
- Chrome (all platforms)
- Safari (iOS) / Safari (Mac)
- Firefox
- Microsoft Edge
Note that totally clearing your browser history can look suspicious. It's rare for someone to have no browsing history at all, so the fact there's nothing there can make you stand out and raise questions. By resetting cookies you're also logging out of all your web accounts, like email, social media, and so on. Make sure you've got all your passwords saved somewhere safe (like a password manager) so you can log in again!
Microsoft has a useful piece of documentation explaining a feature in Windows they call Activity History. It details what it records and how to disable it and clear its history so what you’ve been up to doesn’t pop up by surprise.
If there's an app you use that has stuff in it you don't want others to see, there's often a setting somewhere in the app to clear a cache or clear file history. Chances are you can search on Google a phrase like "clear history (app)" and you'll find an answer.
Don’t forget about the cloud. There's so many cloud based services that store data from your device that it's impossible to give a comprehensive list in a single article, but in general many of them do allow you to log-in on a website or within an app and have a setting or option to clear or remove history, activity, and saved items.
Delete, Reset, Clear, Destroy
Resetting your device before it's sold or recycled doesn’t need to be complicated. Use the built-in tools to do a secure erase and you're set. If your device is broken and the disk can't be removed, be sure to physically destroy the storage portion of that device as that's the only way to be sure the data can't be retrieved.
For situations where you're keeping the device but just want to hide your activity, you've got a lot more work to do. Empty the device's trash/recycle bin, clear the web browser's cache and look in each individual app for a clear or reset setting.
While this info doesn't cover data stored in the cloud – which can sometimes make its way back on to your device even if you've deleted that data from the device itself – it is a guide to scrub your devices up much cleaner. It’s not a comprehensive list of where data can lurk on a computer, but these are the most common places people look.
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