there exists an edge case in string handling (yes, numbers are stored as strings, they just are, don't question it), where null bytes do not terminate a string until the first non-null byte is encountered. due to this, attempting to read the divisor in this case will result in an out of bounds access, and interpret the adjacent section of memory until a null byte as the divisor. in almost all cases, the person's credit card details are stored directly after this region of memory, so that number ends up being used as the divisor. it's actually a pretty common social engineering trick used in phishing attacks to get this information from people