General :: Delete The File And Its Actual Associated Data?

I'm confused about "hard link" feature. I've been learning from my UNIX Academy DVDs training that hard links to a file can be many and each of them is an effective filename for the associated data. So let assume that we have some very sensitive data in a file and we want it to be deleted and file has 20 links. I "delete" a file, but in fact I deleted only one "name" of it. My understanding from the training that data is still there until we delete the last associated hard link. But how can I find the names of all of them? If we have the names, they can be removed one by one. Or may be there's command that can trace all the "names" and remove them at once?