CCleaner for Mac has three methods of secure deletion: a Simple Overwrite (1 pass), Medium Overwrite (7 passes), and a Complex Overwrite (35 passes). A 'pass' refers to how many times CCleaner writes over the spot on the hard drive. The more times CCleaner writes to that spot, the harder the file will be to recover by any means. The drawback is that it will take CCleaner longer to complete the job.
To set the method for secure deletion:
Note: CCleaner can only delete files (including secure deletion) which have not yet been deleted from the Trash.