Software Tool : Alternate File Shredder
License : Freeware/Open Source

With this tools, you can permanently delete files or folders and recovery of files is not possible later on. Also, free space can be shredded (or call it overwrite), so that files that has been deleted cannot be recovered. Note that, you must use this tool very carefully, confirm on what needs to be deleted forever and what need not. So, use this tool at your own risk. 

(link sends you to official site of tool)