a bank's computer system to determine the PIN for an ATM card in an average of 15 guesses. Reverse PIN hoax Rumours have been in e-mail and Internet circulation claiming that in the event of entering a PIN into an ATM backwards, law enforcement will be instantly alerted as well as money being ordinarily issued as if the PIN had been entered correctly. The intention of this scheme would be to protect victims of muggings; however, despite the system being proposed for use in some US states, there are no ATMs currently in existence that employ this software. Mobile phone passcodes A mobile phone may be PIN protected. If enabled, the PIN (also called a passcode) for GSM mobile phones can be between four and eight digits and is recorded in the SIM card. If such a PIN is entered incorrectly three times, the SIM card is blocked until a personal unblocking code (PUC or PUK), provided by the service operator, is entered. If the PUC is entered incorrectly ten times, the SIM card is permanently blocked, requiring a new SIM card from the mobile carrier service. PINs are also commonly used in smartphones, as a form of personal authentication, so that only those who know the PIN will be able to unlock the device. After a number of failed attempts of entering the correct PIN, the user may be blocked from trying again for an allocated amount of time, all of the data stored on the device may be deleted, or the user may be asked to enter alternate information that only the owner is expected to know to authenticate. Whether any of the formerly mentioned phenomena occur after failed attempts of entering the PIN depends largely upon the device and the owner's chosen preferences in its settings. See also ATM SafetyPIN software Campus card Transaction authentication number References Banking terms Identity documents Password authentication