Whistle-blowing

I read in the Gazette of Middlesbrough (on the web) that a firm bought another firm which provides whistle-blowing service. In my dictionary, a whistle-blower is someone who dare say things that another people do not. It seems to me he or she is an informer or a kind of spy. I don’t exactly know the meaning.
If someone can tell me what a whistle-blower is and a whistle-blowing service can be?
Thanks a lot for this information.
It will be better for you to answer in French!