Anti-Spam Software - How It Works- By Paul D Kennedy

There are many types of anti-spam software. However they all fall into one of two major categories:

The first consists of anti-spam software that resides on a mail server, a program that is responsible for receiving, routing and delivering emails, which is operated by an internet service provider (ISP). This software blocks spam before it reaches your PC, laptop or smartphone.

Some spam, however, always gets through. Hence there is a need for the second category of anti-spam software. This runs inside your computer and routes suspected emails to your spam folder where they can be checked and deleted.

Most anti-spam programs, whether they are managed by your ISP or run in your computer, employ a variety of techniques which can be highly effective.

Blacklisting

A blacklist is a list of domain names and email addresses that are known for spam.

Blacklists are maintained by anti-spam programs. When the software encounters an address that is on a blacklist, it flags it as spam.

Content filtering

A content filter is an anti-spam program that contains a database of words and phrases spammers often use. The software analyses the subject line and body of email messages looking for the specific words in its database that indicate spam. Examples of these words include 'Viagra', 'refinance', 'free gift', and so on.

Content filters only block emails containing particular words or phrases. As spammers can easily alter the spelling of words or vary phrases, they are less effective than filters based on statistical methods that are capable of 'learning'.

Bayesian filtering

A Bayesian filter is a statistical technique used to filter emails.

The filter analyses the content of an email message, compares the content to a database of spam characteristics, and calculates the probability that the message is spam. If that probability is above a certain threshold, the email is classified as spam.

The probability that a particular word will occur in legitimate email differs markedly from the probability it will appear in a spam email. Most of us will seldom use a word such as 'Viagra' in our emails, but we will often encounter this word in spam emails.

The great thing about Bayesian filters is that they can adapt automatically to the ever-evolving nature of spam.

When you find spam in your inbox, you should not just delete it. It is much better to hit the spam button which means that you flag it as spam. Your action will be picked up by the Bayesian filter your ISP is probably using, and the filter will add the information to its database. In this way, over time, a Bayesian filter becomes more effective as an anti-spam application.

A Bayesian filter can also be 'tuned' by changing the threshold probability at which it decides whether a particular word or phrase indicates spam. The threshold probability can be varied depending on whether the filter needs to be more or less aggressive in flagging spam. This is usually done by your ISP.

The more aggressive a filter is, the less spam you'll get; but you'll also get more false positives, ie messages that are not actually spam but are flagged as such. If a filter is less aggressive, you'll get fewer false positives but more spam.

Peer-to-peer technology

Peer-to-peer technology is also used in the 'war' against spam.

In this methodology, everyone who uses an anti-spam program can flag certain messages as spam. The program sends this information to a central server, which builds up blacklists.

The anti-spam program on the user's computer is periodically updated by the central server so that it contains the latest blacklists. This can be done manually or automatically on a regular basis. Either way, it is vital that you ensure that your anti-spam software is updated regularly... unless, of course, you enjoy an inbox bulging with spam.

White-lists

White-lists are lists of non-spam email addresses. These are used to tell anti-spam programs that emails from these addresses should always be let through.

Many anti-spam programs will copy the addresses in a user's contact list and assume that these are all legitimate addresses from which the user will be willing to receive email. You can manually add addresses to a white-list just by adding them to your contact list.

Paul Kennedy is the marketing manager of Jupiter Support (Ireland). He can be contacted by email to paul@jupitersupport.ie. You can also go to jupitersupport.ie where you can use chat or Skype to talk with a technician free of charge. Alternatively you can call 0766803006 to speak to a technician and get free advice. Jupiter Support only charges a fixed fee of€19.99 to rid your computer of any and all viruses on a no-fix/no-fee basis.

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