secure delete

I'm running on Windows Vista...

I've just started using BleachBit and so far I'm very impressed. There were two requirements I had when searching for such a tool: the first was the ability to securely shred files and the other was the ability to add my own folders, files and registry entries to the built-in ones. CleanerML is excellent for defining my own cleaners and is far superior to what I'd previously been using in CyberScrub, which I stopped using some time ago due to my dissatisfaction with several product updates.

Further to the earlier discussion about BleachBit's one pass overwrite
functions and whether BleachBit should use more than one pass for it's over wrting pattern:
http://bleachbit.sourceforge.net/forum/bbs-simple-overwrite-not-explaine...

"Studies have shown that most of today’s
media can be effectively cleared by
one overwrite." ?

Can anyone explain what happens why I enable he overwrite function with BB, how does it ensure the data cannot be recovered if I overwrite a file on a hard disk or usb stick?

I do think BB is a great solution for Linux, but how can I trust a functin that just says overwrite with no explanation of what is meant by this term, from a technical stance.

Under BB's preferences options why not enable users to choose standard secure erasing patterns like:

Gutmann method
http://en.wikipedia.org/wiki/Gutmann_method

AFSSI-5020
http://en.wikipedia.org/wiki/AFSSI-5020

DoD 5220.22-M

Hi

How many passes Bleachbit does when you select the "free disk space" option ? 35 passes ? For example Ccleaner with the Gutmann option doeas 35 passes.
Is it as efficient as eraser for windows ? Or "secure-delete" for linux with the command : sudo sfill -v / ?

Regards

Sam