Patent ID: 7617285

Claim:
A computer implemented method for using a dynamically adaptive decision threshold for detecting spam during a current time period, the method comprising: using a computer to perform steps comprising: calculating an estimated spam email occurrence probability for the current time period according to a statistical time series prediction methodology taking into account a previous ratio between a number of emails received in at least one previous time period adjudicated to be clean using a fixed decision threshold and a number of emails received in at least one previous time period adjudicated to be spam using the fixed decision threshold; calculating an adaptive decision threshold to use for the current time period to adjudicate whether emails received during the current time period are spam, the adaptive decision threshold being based on a misclassification cost ratio and the estimated spam email occurrence probability; determining, for each email received during the current time period, a likelihood of the email being spam; adjudicating whether each email received during the current time period is spam by comparing the determined likelihood of the email received being spam to the adaptive decision threshold; comparing, for each email received during the current time period, the determined likelihood of the email being spam to the fixed decision threshold to determine a number of emails received in the current time period adjudicated as spam and a number of emails received in the current time period adjudicated as clean; and calculating a current ratio between the number of emails received in the current time period adjudicated as spam using the fixed decision threshold and the number of emails received in the current time period adjudicated as clean using the fixed decision threshold, the current ratio used to calculate an adaptive decision threshold for a future time period.