Based on the 1974 Privacy Act, When it comes to the legality, SCN numbers are completely legal. However, it should be kept in mind that they can be utilized for credit purposes only and not for deceitful intentions.
FBI: “Credit Privacy Numbers(CPNs) are nine-digit file numbers that follow the same algorithm as Social Security Numbers(SSNs). Currently federal law allows individuals to legally use CPNs for financial reporting and protects those individuals who do not wish to disclose their SSN. Individuals who acquire CPN s are completely responsible for any debt they incur using this number.”