What type of filtering software divides email messages that have been received into two piles, spam and non-spam and then analyzes every word in each email and determines how frequently a word occurs in the spam pile compared to the not-spam pile?

Bayesian filtering

Explanation:

This is a type of filtering software that makes use of Bayesian logic to evaluate every incoming email that you receive, analyzing the header and content of the email to determinate if it is spam or not. It uses a preset of common words that are present in most spam emails, and it categorizes all received emails according to their probability to contain spam in trusted, or not trusted email. These categories are usually set by the user.

In short, Bayesian logic uses the knowledge acquired from past events to try to predict future events. Determinate the probability of success (from 0 to 100%) of a certain activity, according to the result of prior tests. It was first suggested in 1763 after the death of its creator Thomas Bayes, and it is widely spread across several different sciences such as programming, artificial intelligence, physics, etc.

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