Bug in the Wipe Free Space?

Hello,

It is the first time that I access this post (please, excuse my English).

I have three HDs in my PC. I used the option Wipe Free Space in the menu Advanced of CCleaner, but it erased the whole content of my second hard disk (not just the free space)! Why did it make that? Is that a bug? How to avoid?

That's terrible :(

I would like to hear some thoughts on this.