A computer implemented method for identifying aberrant behavior of a financial instrument including: retrieving from a source of market data, closing price, volume and number of transactions conducted for the financial instrument in a selected trading session; recording in computer memory, the closing price, volume and number of transactions conducted for the financial instrument in the selected trading session; identifying a plurality of time periods of different sizes, each of said time periods terminating with the trading session of the financial instrument immediately preceding the selected trading session; obtaining and recording the average and standard deviation of the closing price, volume and number of transactions during each of the time periods; determining whether each of the closing price, volume and number of transactions differs from the average of the corresponding component during each of the time periods by a selected number of standard deviations and for each case in which such a difference is sufficiently large, recording an associated aberrant flag; counting the number of aberrant flags; and identifying and reporting behavior of the financial instrument as aberrant, or not aberrant, based on the total number of aberrant flags counted.