 They needed to add only 50 words to a spam to get it past SpamBayes.However, Wittel and Wu's testing has been criticized due to the minimal header information that was present in the emails they were using; most Bayesian spam filters make extensive use of header information and other message metadata in determining the likelihood that a message is spam.A discussion of the SpamBayes results and some counter evidence can be found in the SpamBayes mailing list archive.