Bitconnectcoin is very notorious on this, they have scammed thousands of millions of millions worth of dollars, their cycle is very shortlived from now on people should learn that MLM and cryptocurrency will not go together, even if defend it as profitable.
Bitconnect was a scam, everyone knows it, but it does not mean that all mlm projects are scam. The majority of ICOs uses afilliate/referral system just to promote their project - it doesn't make them a scam