A spam filter is a piece of software that scans through a message to determine if it is spam or not. Most spam filters work in a very similar way, using a set of rules to try and work out what the message is about and whom it is from. Some are more successful than others.
Types of SPAM Filters :
1. Rules-Based / Bayesian Analysis
2. Content Based
3. White List and Black List
4. Challenge/Response
5. Community-Based
1. Rules-Based / Bayesian Analysis
Rules based systems are the original spam filters. They started life by simply looking for key words or phrases in the message and block based when matches were found. Simple rules based spam blockers are very poor at filtering out spam. They will often block a legitimate message and also let through a good percentage of the actual spam.
A Rules-based spam filter allows the user to determine which email is junk mail and sorts accordingly.
Bayesian Analysis is a relatively new method of filtering spam e-mail. It uses mathematical formulae to analyse the content of a message, learning from the user which is a valid message and which is spam.
A Bayesian spam filter relies on two things to work effectively:
1. How well the Bayesian analysis formulae has been implemented
2. How good a sample of data it has to work with
2. Content Based
Content-based filters block certain words or phrases of incoming mail.
3. White List and Black List
These are very basic types of filters which nowadays are rarely used on their own, but are still used as part of an integrated filtering system comprising some of the other methods shown here.
Whitelist filters will not accept e-mail from any address unless it is on a list of known "good" e-mail addresses.
Blacklist filters, conversely, will allow messages from any address unless the address is on a list of known "bad" sources.
White Lists and Black Lists filter your email either by names in your address book as approved senders, or by blocking known spammers based on a blacklist.
4. Challenge/Response
Challenge/Response filters are characterised by their ability to automatically send a response to an unknown sender asking them to take some further action to ensure their message will be received. This is often referred to as a "Turing Test" - named after a test devised by British mathematician Alan Turing to determine if machines could think.
Challenge/Response filters monitor mail by requiring unknown senders to respond with a security code before allowing their email.
Recent years have seen the appearance of some internet services which automatically perform this Challenge/Response function for the user and require the sender of an e-mail to visit their web site to facilitate the receipt of their message.
5. Community-Based
These types of filters work on the principal of "communal knowledge" of spam. These types of filters communicate with a central server. When a user receives a message that is spam, they simply mark it as such. This information is posted to the central server where a "fingerprint" of the message is added to the database. When enough people have "voted" the message as spam, it will be blocked from user's inboxes in the future.
Community Based anti-spam filters are based on a community of users that report known spammers. Some of the popular email programs use this type of filter. According to Consumersearch.com, this may be a sufficient enough spam filter.
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