well heres the problem for you, you can never really deleate everything. if you want to deleate every thing best way to do it is to get your hammer out and have a good old attack at your hard drive, n buy a new.
but... ok computers as you may be aware can only store 1's and 0's.
so what it does when it deleates something is it just stores certain parts of the hard drive as empty, when there not. it just kinda says liek this bit can be written over next time. so what you need 2 do effectivly is overwrite absolutly everything. so fill your pc up with loads of crap.
and i suppose after a long time every bit of naughty info u had will be replaced with new information.
did that make sence to you?
maby some one else can try explain as well.
hope ive helped
Venney
