Free Spam Filters

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Don’t bother deploying free spam filtering software you find on the Internet -- it is what spam writers use to carry out quality control on their efforts, said one computer security specialist.

“When their spam manages to get through these filters, that’s when they decide to start sending it out,” warned Charles Cousins, managing director of Sophos Southeast Asia Pte Ltd, a leading developer of antivirus software that is now getting into the antispam business.

It was thus a waste of time and money to deploy such spam filters, he said. Users might see an initial dip in spam, but eventually the dip would flatten out and more would begin coming in again.

Spam -- unsolicited and usually undesirable e-mail hawking everything from organ enlargement pills to porn -- was evolving, Cousins said.

Those who created the first generation of spam sent it as plain text, with no effort to disguise what they were sending.

This made them easily vulnerable to text filters, which could be set to search for keywords relating to the erectile-dysfinction pill Viagra, for example, a popular product among spammers.

The second generation of spam saw a new wrinkle, namely attempts to disguise keywords by inserting random letters, numbers, or characters punctuation -- for instance, turning “Viagra” into “v:i:a:g:r#:a.”

This made life more difficult for text-based filters, and they were having to become more complex to adapt to this change.

Now a third generation of spam included what Cousins called HTML (Hypertext Markup Language) based obfuscation.

This consisted of typing not the letters themselves for the word “Viagra,” but the longer HTML character strings that represented each of the letters.

No practical text filter could stop this kind of spam, but the HTML character strings would be decoded if the recipient’s e-mail were HTML-enabled.

The only way to to prevent HTML-obfuscated e-mail getting through would be to turn off HTML decoding of e-mail at the server, Cousins said.

In the future, spammers will resort to graphics in the form of .JPG files attached to e-mail, with the JPEG image carrying the spam text, he predicted.

scource