Free disk space wipers?

[#1]

I mean the programs that claim to overwrite disk free space that might contain recoverable deleted files.
Has anyone used or have opinions on the effectiveness and safety of such?

[#2]

Is this what you are looking for?:
http://download.cnet.com/Darik-s-Boot-and-Nuke-for-CD-and-DVD/3000-2094_4-10151762.html
Darik's Boot and Nuke was the one recommended to me when I asked this question on here a few weeks ago.
It did seem very straightforward to use. Just boot from disk, select Nuke. It takes a long time though.
Has good reviews on the web.

[#3]

CCleaner can be set to do this
http://docs.piriform.com/ccleaner/using-ccleaner/wiping-free-disk-space

[#4]

@poppy.
Thanks :), but I don't want to be so drastic. I want to leave the system intact.
@ Whiffler.Thank you too. I had thought that the option was like poppy's program in its effect, and so avoided it like the plague.have you used CC that way yourself? How did it fare?

[#5]

Sorry, but I don't have any experience of using this feature - only just aware of it's existence.

[#6]

I've used the CCleaner option, and it seems ok.  Certainly doesn't seem to do any harm 
John

[#7]

After I used CCleaner I used Recuva. Several smallish files were listed as recoverable, some classed as excellent. If not all the vast majority were strangely named.

[#8]

hello lucerne. cc wipe disk space is fine and works v well but do use 7 passes. i know this will take around  50 mins..........or more.

another method if you are really concverned is to use recover deep scan then  tick for  overwroite these files  agin you nned to use 7 pass method.
if yopu are still concerned and have time to waste  then run cc wipe again