When you delete a file using the conventional Windows delete method, the file is not actually deleted. Windows simply acknowledges the file is no longer needed and considers it free space, where actually it still exists on the physical storage device.

File Shredder, permanently erases files from your disk without the possibility of them ever being recovered. A vital function because even when you trash files or reformat your hard drive, sensitive data can still be recovered and compromised.
 

PC Optimizer gave you three level for shredding:

Quick (1 overwrite pass) : The fastest, but least secured of the data destruction algorithms. Your data is overwritten with zeroes in a single pass.

Safe (3 overwrite pass) : Three overwrite pass consists of two complimentary overwriting passes followed by a random pass. This is an extra security measure that should prevent any particular recovery program retrieving your data.

Thorough (7 overwrite pass) : Seven overwrite pass will overwrite a file 7 times. It is very secure and should be used for private or general files.

Shredding Operation will delete file permanently.