Not many people know that using Delete in DOS or the Windows Recycle Bin to delete files is not secure. These methods merely remove the file-system's pointer to the file. All the data in those files remains on your computer until the space is reclaimed and overwritten by another file. The remaining data can be easily recovered with any software-recovery program, most of which are free to download. Even if your data has been overwritten, it can still be vulnerable. Using advanced recovery techniques to analyze latent magnetic traces, most any file can be recovered.
Shredder destroys files beyond recovery before deleting them. This means that even if you can recover a file, the data within the file will be totally useless. It overwrites the data with random information a number of times before finally deleting the file. Shredder also cleans all history and temp files.