Anti-Spam Technologies Review - Part 3

Signature

This technology usually requires a community base to fight spam collaboratively. Once a member of the community 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. As spammers usually send out the same spam in bulk, other people in the community who receive an email with the same spam mark will be blocked.

Pros: Signature-based filtering rarely produces false-positives, or legitimate email incorrectly identified as spam.

Cons: The drawback of signature-based spam blockers 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 a member receives a spam message, the system assigns a signature, 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 anti-spam software 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 filter cannot match the email to known pieces of spam.

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