How Spammers Fool Rule-based and Signature-Based Spam Filters

Effectively stopping spam over the long-term requires much more than blocking individual IP addresses and creating rules based on keywords that spammers typically use. The increasing sophistication of spam tools coupled with the increasing number of spammers in the wild has created a hyper-evolution in the variety and volume of spam. The old ways of blocking the bad guys just don't work anymore.

Examining spam and spam-blocking technology can illuminate how this evolution is taking place and what can be done to combat spam and reclaim e-mail as the efficient, effective communication tool it was intended to be.

Heuristics (Rule-based Filtering)

One method used to combat spam is Rule-based, or Heuristic Filtering. Rule-based filters scan email content for predetermined words or phrases that may indicate a message is spam. For example, if an email administrator includes the word "sex" on a company's rule-based list, any email containing this word will be filtered.

The major drawback of this approach is the difficulty in identifying keywords that are consistently indicative of spam. While spammers may frequently use the words "sex" and 'Viagra" in spam emails, these words are also used in legitimate business correspondence, particularly in the healthcare industry. Additionally, spammers have learned to obfuscate suspect words by using spellings such as "S*E*X", or "VI a a GRR A".

It is impossible to develop dictionaries that identify every possible misspelling of "spammy" keywords. Additionally, because filtering for certain keywords produces large numbers of false positives, many organizations have found they cannot afford to rely solely on rule-based filters to identify spam.

Signature-Based Spam Filters

Another method used to combat spam is Signature-based Filtering. Signature-based filters examine the contents of known spam, usually derived from honey pots, or dummy email addresses set up specifically to collect spam. Once a honey pot receives a spam message, the content is examined and given a unique identifier. The unique identifier is obtained by assigning a value to each character in the email. Once all characters have been assigned a value, the values are totaled, creating the spam's signature. The signature is added to a signature database and sent as a regular update to the email service's subscribers. The signature is compared to every email coming in to the network and all matching messages are discarded as spam.

The benefit of signature-based filters is that they rarely produce false-positives, or legitimate email incorrectly identified as spam. The drawback of signature-based filters is that they are very easy to defeat. Because they are backward-looking, they only deal with spam that has already been sent. By the time the honey pot receives a spam message, the system assigns a signature, and the update is sent and installed on the subscribers' network, the spammer has already sent millions of emails. A slight modification of the email message will render the existing signature useless.

Furthermore, spammers can easily evade signature-based filters by using special email software that adds random strings of content to the subject line and body of the email. Because the variable content alters the signature of each email sent by the spammer, signature-based spam filters are unable to match the email to known pieces of spam.

Developers of signature-based spam filters have learned to identify the tell-tale signs of automated random character generation. But as is often the case, spammers remain a step ahead and have developed more sophisticated methods for inserting random content. As a result, most spam continues to fool signature-based filters.

The Solution

When used individually, each anti-spam technique has been systematically overcome by spammers. Grandiose plans to rid the world of spam, such as charging a penny for each e-mail received or forcing servers to solve mathematical problems before delivering e-mail, have been proposed with few results. These schemes are not realistic and would require a large percentage of the population to adopt the same anti-spam method in order to be effective. You can learn more about the fight against spam by visiting our website at www.ciphertrust.com and downloading our whitepapers.

Dr. Paul Judge is a noted scholar and entrepreneur. He is Chief Technology Officer at CipherTrust, the industry's largest provider of enterprise email security. The company's flagship product, IronMail provides a best of breed enterprise anti spam solution designed to stop spam, phishing attacks and other email-based threats. Learn more by visiting enterprise anti spam solution today.

shuttle to Midway Beardstown .. Lockport Chicago limo O’Hare

---

Spam Filters Explained

What do they do? How do they work? Which one... Read More

Learn Simple Strategies That Will Stop Spammers From Bombarding Your Inbox!

Spam filter is the solution that most people resort when... Read More

Six Tips to Get Rid of Spam Email

1. Ignore Spam EmailDo not open an unsolicited email. Spammers... Read More

Sick Of Wading Through Spam?

It's a nightmare isn't it? You fire up your email... Read More

Which Spam Filter Is Best For You?

With the number of spam filtering solutions increasing each week... Read More

E-mail SPAM: Whats The Big Deal?

It absolutely amazes me how many people over-react to receiving... Read More

Is Your Website Blacklisted?

A blacklist, as the name implies, is a list of... Read More

Dealing With SPAM - An E-mail Address Strategy

With SPAM being such a problem it might seem the... Read More

Protecting Yourself With A Porn Filter

The harmful affects of pornography use and addiction are well... Read More

Edating Readers

One of our Australian clients sent out a campaign using... Read More

How Spammers Fool Whitelists - And How to Stop Them

Effectively stopping spam over the long-term requires much more than... Read More

Your Dolphin E-mail Caught In Spam Tuna Net?

Let me ask a couple of questions:If (potential) customers sends... Read More

The War on Spam: Google Fights Back

Google is engaged in a war. It is a war... Read More

Three Faces of SPAM

Like everybody who will ever read this, I get spam... Read More

ANTI-S*P^A#M: Protecting Your Web Sites Email Address(es)

Did you know that there are software programs that view... Read More

Im Guilty Until Proven Innocent

No doubt about it."Spam" (unsolicited commercial email) threatens to paralyze... Read More

How To Stop Spam

I imagine you have seen, heard about, or already know... Read More

The Definition of Spam

Spam can bring down your website faster than a speeding... Read More

Ignoring These Tips Could Result in an Inbox Full of Spam

Although there still seem to be some differences among the... Read More

Avoid, Shun, Thwart, Prevent, and then Filter Spam

Email is rapidly becoming the standard means of communication among... Read More

Junk Mail Works!

Junk mail works. Why does it work? How does it... Read More

Winning the War On Spam

For years I didn't worry much about spam.But lately it's... Read More

Spam with Typos: Why Do They All Have Spelling Errors?

A friend asked me: I don't get it. Why do... Read More

Protecting Your Business From Spam

Even being as careful as possible with my email address,... Read More

Why Is Spam Such a Problem?

Spam can be a lot more damaging than you might... Read More

Green Bay Hummer H2 SUV rentals ..