> Wilson suggests contacting references not provided by the candidate. That can be a major breach of privacy.

He mentions it casually, so I don't know what exactly he meant.

I know that I did as he recommended -- but before I contacted a reference not provided by the candidate, I asked them if it was ok to make that contact. In most cases, the answer is "sure, go ahead", or "that's ok, I guess". When the answer is "I rather you wouldn't", the story is often interesting and relevant to your hiring decision.