Either since when, but Bitcoin is indeed a lot of black market that uses illegal smells of various services and goods that are difficult for us to find because we can get illegal using Bitcoin as a transaction tool. because bitcoin is private, so the recipient and sender of the hidden bitcoin identity is very profitable in their business because of illegal transactions.
if you don't believe me or just curious, just check there, go to the internet side deepweb which isn't easy to open ... just visit it, just look for the method on google.