A program used to detect unsolicited and unwanted e-mail and prevent spam messages from getting into a user's inbox. Like other types of filtering programs, a spam filter looks for certain criteria on which it bases judgments. For example, one method is to set the spam filter to watch for particular words in the subject line of e-mail messages and then exclude these from your inbox. This method is not very effective, however, because it often omits perfectly legitimate messages (false positives) and still lets actual spam come through. Another method which is more sophisticated is using Bayesian filters (or other heuristic filters) in an attempt to identify spam through word frequency or suspicious word patterns.