Actually, the "delete" operation in Windows only removes bits of information from files so they appear deleted in OS. It is easy to retrieve those files using aforementioned specialized file recovery software.
In order to remove, or shred files permanently from your system you have to use a program that is capable of rewriting the files with random series of binary data multiple times. This process is often called shredding. That way, the actual content of the file has been overwritten and the possibilities to recover such a shredded file are mostly theoretical.
File Shredder has been developed as fast, safe and reliable tool to shred company files. I believe this utility should be available to anyone for free and that permanent and safe removal of confidential documents is a matter of basic right to privacy.
In File Shredder you can choose between 5 different shredding algorithms, each one gradually stronger than the previous one. It also has integrated Disk Wiper which uses shredding algorithm to wipe unused disk space. More on options of File Shredder check Online Help page.
Reference from: http://fileshredder.org/
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