“Whoo-hoo-hoo, look who knows so much. It just so happens that your friend here is only MOSTLY dead. There’s a big difference between mostly dead and all dead. Mostly dead is slightly alive.” Miracle Max in The Princess Bride.
And there’s a big difference between mostly deleted and all deleted.
Deleting a file in Windows using the File Explorer, or an application, does not delete the file. It moves the file to the Recycle Bin. From there, you can restore the file to its original location unchanged. Emptying the Recycle Bin will not erase the file contents from your internal disk drive. You can still recover the file until a new file overwrites its contents on the drive. If the file contains sensitive content, this could present a privacy risk. The same is true on macOS. Sending a file to Trash does not delete the file contents.
To completely and securely delete a file, a secure file wipe is required. A secure file wipe overwrites the physical location of the file on the disk with random characters obscuring the original contents.
To securely delete a file in Windows, I recommend Bleachbit. It’s free. You can find it at: https://www.bleachbit.org/ .
In macOS, use “Secure Empty Trash” to wipe file contents.
No special actions are required on iOS or Android.
During normal operations, your internal disk will accumulate bits and pieces of files in what is called “free space”. Until the operating system writes to it, the “free space” remains unaltered, allowing for recovery of old bits of data. To remedy this vulnerability, it is prudent to occasionally wipe the free space and overwrite the old data.
Bleachbit provides this capability on Windows. On macOS, use the Disk Utility to wipe free space. Note that on a large disk drive, wiping free space can take some time.
If deleted files containing sensitive data, make sure they are completely and securely wiped from your disk drive.
Information provided in this post is subject to the disclaimer in the first post of this series.