Battle of wills

摘要

Do you want to buy Vi@gra? Need to enlarge part of your anatomy? Anyone who uses email will be familiar with phrases like these, distorted to fool spam filters by marketers who want us to buy their products online. Designing spam has become an art form, constantly evolving to beat filtering systems. The most basic way of doing this is to use "digit words" where numbers or symbols replace letters in the middle of a word. They are designed to fool lexical analysis tools that examine the word content of an email and recognize common "spam" terms. However, as the most common digit words (such as Vi@gra) are now recognized by most lexical filters, foreign characters and accented letters are starting to appear in their place. More sophisticated (but still common) techniques include HTML obfuscating, which is placing HTML tags that are invisible to the reader in the middle of words. For example, if a spam filter is set up to recognize the word enlargement.or digit words like it, a spammer might try to avoid this by replacing "enlargement" with "enlargement." Once the email appears on the recipient's screen, the becomes invisible so the reader will only see the word "enlarge-ment."This technique is used to fool lexical analysis filters.