The popular standard protection service providers offer is the Personal Identification Number (PIN). This four-digit code prevents unauthorized access to the SIM card, ensuring data security.

A PUK code is required if a GSM SIM card was locked after entering the wrong PIN code three times in a row. Entering a wrong PUK code ten times in a row disables the SIM card permanently.

This is a numeric code which must be entered each ... In GSM mobile phones, the PIN is normally associated with the SIM card (not the phone) and must be entered each time the phone is switched ...

[Jason Gin] wanted to reuse the SIM card that came with a ZTE WF721 ... way backwards and determine the unlock command and its PIN code. It turns out the PIN was even being sent over the wire ...