To erase files recursively in a specific directory with best security and make it almost impossible to recover any of the files in that directory, run the following command:
find . -type f | while read file ; do shred --verbose --remove --zero -n 10 $file ; done
I say almost because the author didn’t seem to have ruled out the possibility of recovering the files, but my guess is that only very specialized labs and governments would be able to afford attempting this.
Important Note: Be careful with this command. You really need to NOT FORGET to do the command