Overwriting the hard drive's data so the data cannot be recovered is the most common method used to clean hard drives. This process cleans the data on the hard drive by overwriting the data with other data so the original data cannot be recovered.
There are various versions of free software that can be used to securely "wipe" a hard drive and/or USB flash drive.
- Darik's Boot and Nuke (DBAN) - Good for any magnetic hard disk drive, not for USB flash drives or SSD drives
- Roadkill's Disk Wipe - Good for USB flash drives and easy to use
If the drive is inoperable and can't be wiped with a software solution, physical destruction by the following methods can either make the drive completely unusable or destroy the data.
- Breaking, drilling, and/or pulverizing the actual disk
- Using a magnetic degausser approved by the Department of Defense