SecretShredder 0.4.2 for Mac was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. This Mac app was originally designed by mizog.com. We recommend checking the downloaded files with any free antivirus. The software lies within System Tools, more precisely File Managers.
From the developer:
Files can remain on your Mac even after they have been deleted or moved to the trash. Indeed using techniques like magnetic force microscopy data can be retrieved even after your drive has been formatted.
The only sure way to delete files and clean up your free disk space ( where files previously moved to the trash may still lie ) is to overwrite them many times using well-known bit patterns so that they can never be recovered.
You may want to check out more software for Mac, such as pdf-FieldMerge, getTunes or Creature, which might be related to SecretShredder.