Home
>
Spam Blocking
>
Spam Filters Explained

Spam Filters Explained

What do they do? How do they work? Which one is right for me? By Alan Hearnshaw

Spam is a very real problem that many people have to deal with on a daily basis. For those that have decided to do something about it and start to investigate the options available in spam filtering, this article provides a brief introduction to your options and the types of spam filters available.

Despite the bewildering array of spam filters available today, all claiming to the best one "of its kind" there are really just five filtering methodologies in general use today and all products rely on one, or a combination of these:

Content-Based Filters

"In the beginning, there were content-based filters."

These filters scan the contents of the and look for tell-tale signs that the message is spam. In the early days of spamming it was quite simple to look out for "Kill Words" such as "Lose Weight" and mark a message as spam if it was found.

Very soon though, spammers got wise to this and started resorting to all kinds of tricks to get their message past the filters. The days of "obfuscation" had begun. We started getting messages containing the phrase "L0se Welght" (Notice the zero for "o" and "l" for "i") and even more bizarre ? and sometimes quite ingenious ? variations.

This rendered basic content-based filters somewhat ineffective, although there are one or two on the market now that are clever enough to "see through" theses attempts and still provide good results.

Bayesian Based Filters

"The Reverend Bayes comes to the rescue"

Born in London 1702, the son of a minister, Thomas Bayes developed a formula which allowed him to determine the probability of an event occurring based on the probabilities of two or more independent evidentiary events.

Bayesian filters "learn" from studying known good and bad messages. Each message is split into single "word bytes", or tokens and these tokens are placed into a database along with how often they are found in each kind of message.

When a new message arrives to be tested by the filter, the new message is also split into tokens and each token is looked up in the database. Extrapolating results from the database and applying a form of the good reverend's formula, know as the a "Naive Bayesian" formula, the message is given a "spamicity" rating and can be dealt with accordingly.

Bayesian filters typically are capable of achieving very good accuracy rates (>97% is not uncommon), and require very little on-going maintenance.

Whitelist/Blacklist Filters

"Who goes there, friend or foe?"

This very basic form of filtering is seldom used on its own nowadays, but can be useful as part of a larger filtering strategy.

A "whitelist" is nothing more than a list of e-mail addresses from which you wish to accept communications. A whitelist filter would only accept messages from these people and all others would be rejected

A "blacklist", conversely, is a list of e-mail addresses - and sometimes IP Addresses (computer identification addresses) - from which communications will not be accepted.

While this may seem like a good idea from the outset, a whitelist methodology is too restrictive for most people and, as virtually all spam e-mails carry a forged "from" address, there is little point in collecting this address to ban it in future as it is very unlikely to be the same next time.

There are bodies on the internet that maintain a list of known "bad" sources of e-mail. Many filters today have the ability to query these servers to see if the message they are looking at comes from a source identified by this Internet-based blacklist, or RBL. While being quite effective, they do tend to suffer from "false positives" where good messages are incorrectly identified as spam. This happens often with newsletters.

Challenge/Response Filters

"Open sesame!"

Challenge/Response filters are characterised by their ability to automatically send a response to a previously unknown sender asking them to take some further action before their message will be delivered. 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".

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.

Critics of this system claim it to be too drastic a measure and that it sends a message that "my time is more important than yours" to the people trying to communicate with you.

For some low traffic e-mail users though, this system alone may be a perfectly acceptable method of completely eliminating spam from their inbox - one step above the "Whitelist" system outlined above.

Community Filters

"A united front"

These types of filters work on the principal of "communal knowledge" of spam. When a user receives a spam message, they simply mark it as such in their filter. This information is sent to a central server where a "fingerprint" of the message is stored.

After enough people have "voted" this message to be spam, then it is stopped from reaching all the other people in the community.

This type of filtering can prove to be quite effective, although it stands to reason that it can never be 100% effective as a few people have to receive the spam for it to be "flagged" in the first place. Just like its similar cousin the Internet black list (RBL), this system also can suffer from "false positives", or messages incorrectly identified as spam.

Hopefully you are now armed with a little more information to be able to make an informed decision on the best spam filter for you.

For further information, consider reading the reviews and articles found at http://www.whichspamfilter.com

Alan Hearnshaw is a computer programmer and the owner of http://www.whichspamfilter.com, a web site which conducts weekly in-depth reviews of current spam filters, provides help and guidance in the fight against spam and provides a useful community forum. http://www.whichspamfilter.com

Batchtown Chicago prom limo .. Lockport Chicago limo O’Hare

In The News:

A virtual private network can help ensure your information remains security and your privacy remains intact. Kurt the CyberGuy explains.

Stay up to date on the latest AI technology advancements and learn about the challenges and opportunities AI presents now and for the future.

Artificial intelligence-based cameras are giving air defense operators unprecedented capabilities in monitoring and protecting airspace.

Apple's iOS 18.1 Inactivity Reboot automatically reboots your iPhone if it hasn't been used or unlocked for more than three days, providing better data protection.

An inventor designed rooftop solar panels for a Tesla that draws solar energy while the car is parked, adding travel mileage without plugging in.

There are currently no laws governing what artificial intelligence can and cannot do with the information it gathers; here are 10 things to avoid telling AI chatbots to keep yourself safe.

A credit union with over 240,000 members recently revealed it was targeted by cybercriminals, resulting in a data breach that was part of a two-month attack by hackers.

Scammers have become skilled at creating convincing fake websites that can easily fool unsuspecting users. The CyberGuy offers tips to protect yourself.

Stay up to date on the latest AI technology advancements and learn about the challenges and opportunities AI presents now and for the future.

CAPTCHAs, which are used by websites to confirm whether users are people or bots, are harmless, but hackers are using them to infect PCs with malware.

Hackers recently leaked personal information of about 500,000 Americans and stole patient medical records that included lab results and insurance details.

The holiday season sees a rise in mobile shopping scams. Tech expert Kurt “CyberGuy" Knutsson helps you learn how to stay safe.

Tech expert Kurt “CyberGuy" Knutsson says a VPN enhances online banking security by encrypting data and protecting privacy.

Beware of these six sneaky holiday scams. Tech expert Kurt “CyberGuy" Knutsson gives you tips to avoid falling victim.

Tech expert Kurt “CyberGuy" Knutsson reveals how to securely back up and factory reset your Android to protect your privacy and data.

Artificial intelligence is making life easier for cybercriminals, allowing them to create elaborate scams to trick people. Kurt the Cyberguy explains how to protect yourself.

Cut through all the digital clutter and delete multiple emails from your Android simultaneously. Kurt the CyberGuy explains how it's done.

Tips to prevent your holiday decorations from being stolen

Stay up to date on the latest AI technology advancements and learn about the challenges and opportunities AI presents now and for the future.

Kurt "CyberGuy" Knutsson lays out the immediate steps you should take if your phone has been hacked and your personal information becomes vulnerable.

Fraudsters are sending people bogus invoices through PayPal as part of a sneaky scam that is going around; here's how to protect yourself from being fooled.

A former Colgate-Palmolive employee was shocked to discover $750,000 had been drained from her 401(k) account. "CyberGuy" offers tips on how to prevent identity theft.

Electric vehicle maker Harbinger recently showed its electric delivery truck can handle icy roads with agility and stability in winter.

To make the busiest time of year more manageable, here are some tricks for tracking your packages, taking quality family photos and curating the perfect Christmas playlist.

Kurt "CyberGuy" Knutsson explains how to keep your online Amazon gift purchases a secret from loved ones or friends this holiday season.

Spam Filters Explained

Spam Blocking