Editing Email spam (section)

===Obfuscating message content===
Many spam-filtering techniques work by searching for patterns in the headers or bodies of messages. For instance, a user may decide that all email they receive with the word "[[Sildenafil|Viagra]]" in the subject line is spam, and instruct their mail program to automatically delete all such messages. To defeat such filters, the spammer may intentionally misspell commonly filtered words or insert other characters, often in a style similar to [[leetspeak]], as in the following examples: {{mono|V1agra}}, {{mono|Via'gra}}, {{mono|Vi@graa}}, {{mono|vi*gra}}, {{mono|\/iagra}}. This also allows for many different ways to express a given word, making identifying them all more difficult for filter software.

The principle of this method is to leave the word readable to humans (who can easily recognize the intended word for such misspellings), but not likely to be recognized by a computer program. This is only somewhat effective, because modern filter patterns have been designed to recognize blacklisted terms in the various iterations of misspelling. Other filters target the actual obfuscation methods, such as the non-standard use of punctuation or numerals into unusual places. Similarly, HTML-based email gives the spammer more tools to obfuscate text. Inserting HTML comments between letters can foil some filters. Another common ploy involves presenting the text as an image, which is either sent along or loaded from a remote server.