## Bayesian Filters

Written by Debbie Hamstead

A common problem with filters is fact that they are a one-size-fits all solution to SPAM. The rules are concrete and only change based on input from updates from Anti-spam service.

SPAM changes too quickly to make that method effective. Additionally, what is SPAM to you may not be to someone else. That is where Bayesian filters come in.

They are very effective at eliminating SPAM and have very low false-positive rates for their users.

Bayesian filters are based on Bayesian logic, a branch of logic named for Thomas Bayes, an eighteenth century Mathematician.

This type of logic applies to decision making by determining probability of a certain event based on history of past events.

Using this as a model seemed a logical step for SPAM filtering. If you can predict what SPAM will look like now based on what is has looked like in past, you are halfway to solution.

To finish solving problem, Bayesian filters were developed to be dynamic and continue to be effective as SPAM changes.

Bayesian filters are content based. They look for characteristics in each email that you receive and calculate probability of it actually being SPAM.

These characteristics are generally words in content and header file information that each email contains. They can also include common SPAM HTML code, word pairs, phrases, and location of a phrase in body of email.

Typical words in SPAM would be "Free" and "Win", while "humility" would probably not appear. The filter begins with a 50% neutral score for email, and then adds points for SPAM characteristics.

Likewise, deductions are made for non-SPAM characteristics present. The total score is calculated and then action is taken based on its likelihood of being SPAM.

The filter does not assume that all arriving email is bad, rather that all email is neutral and should be considered equally.

Written by Debbie Hamstead

Spam only occurs when spammer is able to get your email address. They have a variety of methods for doing this, some legal and some not.

Either way, result is same. You have become a spam victim. The single most important action that you can take to prevent spam from occurring is to keep your email address off of those lists.

There are a number of ways that this can be accomplished, starting with never giving out your address to anyone whom you do not know or are not conducting business with.

You wouldn't broadcast your phone number over internet, so why is your email any different? Be careful when putting your email address into directories or other form of printed lists.

Those directories could end up on internet giving millions of people access to your email.

If, for example, you are a member of your alumni association and they decide to build a webpage with that information, your address has been exposed however unintentionally.

Make sure of privacy practices that are in place with any organization that you give your email address to.

If you are willing to give them payment information, then you should feel comfortable giving them your email.

However, fact that they will process sale in accordance with law does not mean that they won't sell lists to spammers.

The sale of goods over internet is regulated and enforced much more stringently than address list distribution. Often it is just too difficult to prove.

The site may ask you if they can share your information with their "partners" or "affiliates". These are simply companies to whom they sell information for purpose of advertisement - spammers.

This box is almost always automatically checked for yes, so make sure you uncheck it before submitting your order.

Perhaps you would like to join a mailing list, newsgroup, or register with a certain website. Before doing so, read privacy policy of website involved and make sure that they will not sell or share your information with anyone else.

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