# Bayesian filter

What is Bayesian Filter?
A Bayesian filter is a computer program that uses Bayesian logic or Bayesian analysis, which are synonymous terms. It is used to assess the header and content of email messages and determine whether it is spam - unsolicited email or the electronic equivalent of bulk mail or junk mail. A Bayesian filter is best used in conjunction with anti-virus software.

A Bayesian filter works with the probabilities of certain words that appear in the header or in the content of an email. Certain words indicate a high probability that the email is spam, such as Viagra and Refinance. The filter does not start with the probability that a word indicates a high probability of spam. Users have to manually identify the email as spam. If enough occurrences of the word are found and the email is identified as spam, the Bayesian filter 'learns' to identify the word using probability functions. It does the same thing with many other words and phrases.

Over time, the Bayesian filter becomes more and more effective in identifying spam for a given user. When the probability reaches a certain threshold, e.g. B. 95 percent, the email is identified as spam and often moved to a junk folder (or sometimes even automatically deleted). The user can view it periodically and decide whether or not to delete it. Alternatively, some spam programs move the program to a quarantine location where users can view the email and review the software's decision.

The initial 'training' can often be refined to avoid false positives or false negatives if false judgments are found. This allows the software's Bayesian filter to adapt to the constantly evolving type of spam.

Some spam filters use heuristics in conjunction with the Bayesian filter. Predefined rules are set up by the user to further improve the accuracy of identifying emails as spam. These rules can include the number of occurrences of a given word, eliminate or ignore neutral words like 'that', 'a' or 'some', or identify sequences of works like 'Viagra is good for' as opposed to using a probability function for all four individual words.

Spammers can use a technique called Bayesian intoxication to reduce the effectiveness of Bayesian filtering spam. Some techniques include injecting legitimate text from messages or literary sources, using random harmless words rarely found in spam, or even replacing text with images.

Many email clients disable the display of images for security reasons. As a result, the spam can reach fewer recipients.

A Bayesian filter using Bayesian logic can be used to classify any type of data. Medicine, science and technology have all found their uses. Interestingly, scientific researchers have speculated that even the human brain can use Bayesian logic methodology to classify stimuli and determine specific responses.

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