Most mobile phones offer the feature of PIN protection.
After switching on the phone, if the PIN security function is active, the user is required to enter a 4-8 digit PIN to unlock the SIM card and connect to the mobile network.
If the wrong PIN is entered more than three times, the SIM card will become locked.
If the wrong PUK is entered ten times in a row, the SIM card will become permanently blocked and unrecoverable, requiring a replacement or, in rare cases, can be recovered by the provider when the PUK code is forgotten.
Mobile phone users are therefore advised by most providers to keep their PUK written down in a safe place separate from the device.