How do I wipe free space on my computer?

On the Windows tab, select the Wipe Free Space check box. CCleaner displays a warning about extra time. Click OK. Run CCleaner as usual. Method 2 (Manually wipe with Drive Wiper): Select Tools > Drive Wiper; Choose the type of wipe you require: Free Space Only will leave your normal files intact; Entire Drive will erase all of the files on the drive.
For More Information Please Refer:
https://www.ccleaner.com/docs/ccleaner/using-ccleaner/wiping-free-disk-space
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