NeedHelp

Hi there, I just wanted to know what happens when you do the secure file deletion NSA Overwrite (7 pass)??? I ran cclean on that setting and it took sometime so i stopped over 7 bars passed (note - you'll understand that i mean when you do it) and it shows that i deleted over 815 mb of something... If someone can just please give me a straight forward answer to what each Secure Deletion 1/3/7 pass do. Thanks a lot...sorry if i dont make sence this is a new language for me.