Abstract: An improvement in structure and credit account access security employing method and means for ensuring that repeating an exact access code which was successful in accessing the account will be unsuccessful at the next or subsequent tries. The user enters a PIN code in accordance with a prescribed, but variable, sequence, the sequence being different for each transaction from the previous transaction. The user inputs the PIN by entering a sequence of alphanumeric symbols in accordance with a prescribed "start" sequence of symbols for recognition as a proper 4-digit PIN for a first transaction. The user must enter a new PIN to access the same account on subsequent tries. Preferably, the sequence of symbols comprising the PIN has only one symbol different from the "start" sequence for recognition as a proper PIN for a second transaction and the third transaction may require yet a third sequence of alphanumeric symbols comprising a third PIN.