What is MCK?

MCK, or Master Control Key, is a code that is used to unlock a mobile phone’s SIM card when it is blocked due to a user entering the wrong PIN code multiple times. When a user enters the wrong PIN code three times in a row, the SIM card is blocked, and the phone can only be used to make emergency calls. To unblock the SIM card, the user will need to obtain the MCK code from their carrier.