An error at First National Bank of Chicago resulted in the balance of 800 customers being inflated by a total of $763 billion.
Inadequate testing. Bank updated ATM transaction software with new message codes. Message codes were not tested on all ATM protocols, resulting in some ATMs interpreting them as huge increases to customer balances.
Inadequate testing. Navigation package inherited from Ariane-4 without proper testing. New rocket flew faster, resulting in larger values of some variables, resulting in an attempt to convert a 64-bit floating number into a 16 bit integer. Code was caught and action taken was to shut down navigation system.