The FBI has issued a warning to Americans against using unregistered cryptocurrency money-transmitting services, which may be targeting smart-contract-driven privacy tools. The Bureau urges the use of registered Cryptocurrency Money Services Businesses that comply with existing KYC and AML laws. This announcement follows recent law enforcement operations against unlicensed cryptocurrency services. Meanwhile, the co-founders of Bitcoin wallet and crypto mixing service Samourai Wallet have been arrested on charges of money laundering. The FBI's warning and the arrests have sparked debates about the definition of a Money Services Business in the crypto sector.