You are required to register your card for MasterCard's SecureCode with your respective bank. Almost all South African cards are preregistered for 3D Secure by your bank, regardless if they have been used online before. Only corporate cards that use static passwords still require the cardholder to activate, but this is determined by the bank during the transaction.
If, for some reason, your card is not registered, 3D Secure will prompt you to activate it during the transaction. You can activate your cards through your online banking profile or simply call your bank directly to help you.