When you delete files in Windows, they can be easily recovered. Windows deletes the files in the system, but they remain on your hard drive until they are replaced with new data. 
Although on SSD, it is harder to retrieve files from hard drives because of the SSD control and garbage collection, all deleted data is not completely deleted by default.
So if you've deleted some sensitive data and want to make sure it can't be recovered for any reason, below we describe a way to delete it that will make it disappear forever, and that too without tools third parties.
In Windows XP, Vista, Windows 7, Windοws 8 και Windows 10, υπάρχει ένα βοηθητικό program console called "encryption" or "cipher".
It is a command line tool to encrypt files using EFS (File Encryption System). But this tool has an additional function. It can "rewrite" and clear again in the free space, so that all the data it contains will be deleted safely.
To achieve this, the cipher performs 3 passes. With the first pass, it fills the empty space with zero data, the second fills the empty space with numbers 0xFF, and the final pass fills it with random numbers.
This process may take time, depending on how large your disk is and how much free space it contains.
To clear the free space safely with Cipher.exe, do the following:
At search of Windows look for cmd.exe. When the black icon appears, right click on it and open it as Administrator.
Type the following command and press Ender:
cipher / w: C
Replace “C” with letter of the drive you want to clean up free space on, and wait for it to finish.
Cipher.exe is a great way to safely clean your free space if there is any real reason. Note that on SSDs, additional recordings in the long run may slightly reduce the life of discs. But your free space will be deleted safely, and no one will be able to recover your sensitive files or know what activities you have done on the computer.
