At YouTube we have developed one of the most sophisticated anti-piracy systems in the world—Content-ID. It allows the largest record companies in the world and small independent artists alike to give us copies of their music, which we then scan against the corpus of data on YouTube. This way we can identify, on behalf of those artists, uploads to YouTube of their content. Then we give those artists the opportunity to monetize the uploaded content.
On March 1st, 2012. See this statement in context.