An erroneous result. For example, a discovery and classification tool using regular expressions might mark every 9-digit sequence as a US Social Security number. However, US mailing ZIP+4 codes are also represented as 9-digit numbers. The solution might erroneously classify all ZIP+4 codes as Social Security numbers. All those classifications are false positives. The opposite of a false positive is a false negative. An example of a false negative is a US Social Security number that was not detected by the solution, even though it was a 9-digit sequence.