Be sure to wipe your drives, devices, and anything that potentially contained sensitive files before getting rid of it. Whether you’re disposing of it, selling it, or giving it away — securely erase your data first.
This is necessary because it’s possible to recover deleted files from many types of drives. The data isn’t always deleted from the drive.
USB Drives, External Hard Drives, and SD Cards
This is necessary for USB drives and external hard drives. Yes, even though your USB drive contains solid-state flash memory — and even though your external hard drive might contain a proper solid-state drive — you need to worry about this.
TRIM isn’t supported via the USB interface, which means someone could potentially recover sensitive files from an old USB drive after you get rid of it.
To wipe an external drive on Windows, you can use one of many drive-wiping tools. CCleaner is a particularly easy one to use — you just need the free version. Insert the USB drive or plug in the external hard drive, open CCleaner, and use the Tools > Drive Wiper feature.
Bear in mind that this will reduce your drive’s lifespan, especially for cheap flash drives. But, if you’re about to dispose of the drive, that’s fine.
On a Mac, open the Disk Utility application, select the drive in the list, and click the Erase heading. Click Security Options and tell it to erase the drive once, and then erase it.
Laptops, Desktops, and Internal Hard Drives
On a laptop or desktop, your internal hard drives only need to be wiped if they’re mechanical hard drives or hybrid hard drives. When you delete a file on a solid-state drive, the file is automatically wiped from the drive due to TRIM — this helps keep your SSD speedy.
The below tricks are only necessary if you’re using a mechanical or hybrid hard drive. Don’t do this for solid-state drives — it’s both a waste of time and will cause unnecessary wear to the SSD.
On Windows 8 and 8.1, you can simply choose the “Reset your PC” feature and tell Windows to securely erase the drive. Choose the “Fully clean the drive” option to ensure none of your files can be recovered later.
If you’re using Windows 7, Linux, or another operating system, you can boot your computer from a tool like DBAN. This tool will boot up and erase your computer’s hard drives, overwriting them with random data. You’ll have to reinstall Windows or Linux afterwards before anyone can use the computer again, of course.
And remember, you don’t need to do several wipes — just the one wipe will do.
Smartphones and Tablets
Apple’s iPhones and iPads use encryption, which means you can just reset them with the “Erase All Content and Settings” option and your personal data will be inaccessible. Any fragments of data are stored on the device in encrypted form, and no one can access them.
On Android smartphones and tablets, encryption has historically not been enabled by default. That means simply performing a factory reset won’t help — sensitive personal data may be left on the phone’s internal storage.
To securely wipe an Android phone or tablet, first go into its settings and encrypt the storage. You can then erase the device and restore it to factory settings. Because the data stored on the device was encrypted before you performed the factory reset, the data stored on the device will be scrambled and incomprehensible.
Encryption Ahead of Time Also Works
You could also just enable full-disk encryption ahead of time. When you use encryption, your data can’t be recovered without your encryption passphrase. Any bits of leftover data and other files will be on the drive in an encrypted, scrambled state. People using data forensics software won’t be able to pick out any fragments of data.
If you have a CD or DVD you want to remove sensitive files from, you can erase it if it’s rewriteable. Otherwise, be sure to physically destroy the CDs or DVDs before disposing of them. This could mean grabbing a pair of scissors and cutting them into one or more parts.