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In mobile telephony, a Personal Unblocking Key (PUK) is a numeric password used to unblock a SIM card. A SIM card can become blocked if it has password protection activated (via the SIM PIN feature) and an incorrect PIN has been entered three times. The PUK is available from the cellular service provider who supplied the SIM card. If an incorrect PUK is entered ten times in a row, the SIM card can become permanently unusable. PUK is also known as PUC (PIN Unblocking Code).