I know that this may be this may be quite annoying for some experts ... hopefully annoying enough to flame me. But I have heard too much about nessus. This thing comes along with many Linux distros. But after all what is nessus? Google and other searches tell it is a network vulnerability scanner. However I see some people tell that nessus is a DATA recovery software. While some say that it runs on *nix boxes but some say that runs even on Windows.

So is nessus a Network vulnerabilty scanner or Data recovery solution or both?

What OSes does it run on? Does it run on only *nix or Windows or both or even on others like Mac?

Thanks in advance.