Shredo is a beautiful and functional file shredding utility. It permanently shreds files, folders and external volumes' contents to keep information secure and impossible for anyone to retrieve.
Secure Empty Trash feature is also available.
Depending on security level and data erase speed, you have 3 shredding methods at your disposal:
Offers good security and quickest erase of data. It deletes access information to your files and writes random bytes over the data ONCE.
Slower speed, but better security than 1-pass.
Writes over data 7 times, based on US Department of Defence (DoD) 5220-20 M standard algorithms.
Slowest, but offers best security.
Erases file access info and writes over the data 35 times, based on the Gutmann method for deletion.
Shredo supports external volumes and flash drives, but depending on their size and method selected, shredding time many vary.