Secure deletion on SSDs, USB flash drives, and SD cards is very hard! This is because these types of drives use a technique called wear leveling and do not provide low-level access to the bits as stored on the drive. These instructions apply only to traditional disk drives, and not to Solid State Drives (SSDs), which are standard in modern computers, USB keys/USB thumb drives, or SD cards/flash memory cards. The instructions below should only be used for securely deleting data from spinning drives. More information is available on encrypting with FileVault 2.
If you encrypt your entire drive, you don’t have to worry much about doing secure deletion since the master encryption key is protected with a password that you control, and that you can change or erase to make data on the drive irretrievable. We highly recommend you take this step to protect your data. Note: Modern versions of macOS will prompt you to use FileVault 2 to encrypt your entire drive.
