Best (preferably free) tool to wipe deleted files on an NTFS filesystem [duplicate]
Solution 1:
If you run Sysinternal's SDelete with the -z argument, it will cleanse free space on the given drive.
sdelete -z c:
This is a good solution if you want to run as a batch file every so often, or if you just prefer a command line tool.
Solution 2:
Ccleaner - check the Advanced option, Wipe Free Space.
Ccleaner is freeware, I recommend using the Portable or Slim version (the default installer will install a browser toolbar).