25. The computer-readable medium of claim 18 , the program code to configure the one or more processor to generate a negative usefulness prediction value further comprising program code to configure the one or more processors to: determine the negative usefulness prediction value using a product, P, of a feature vector that identifies the features extracted from the given URL and a weighting vector that includes a weighting for each of the features extracted from the given URL to generate the negative usefulness prediction value using a formula: 1'1[1/(1+e −P )].
26. The computer-readable medium of claim 25 , the weighting vector including an intercept weighting that corresponds to the count of the positive URLs in the training set.