Trick five: Light reading

Taking it a step further than the word salad technique, some spam messages contain entire extra sentences and paragraphs added to the message ? with the same aim to add in good words and phrases to skew the spam filters' evaluation of the entire message. The use of complete sentences makes it more difficult for the filter to exclude the good words.

Trick six: Tiny text

Another way in which spammers trick spam filters is by changing the size of the font of some letters, yet making those that make up a message readable. The recipient can read the message, while the spam filter sees a line of gibberish.

Trick seven: Scrabble spam

While the human brain can decipher a scrambled message like "Crteae a more ppsorerous future for yuoserf", spam filters cannot. And because slang, acronyms, abbreviations and human error feature regularly in our legitimate daily emails, it is not feasible to program spam filters to block emails with misspelled words in them. By scrambling the letters in words, spammers are often able to get past spam filters.

Trick eight: Bad words in disguise

Yet another way in which spammers get around spam filters is by using symbols, special characters and different character sets to spell out words. For example, VIAGRA becomes \/!?GR? ? and it is estimated that there are over 600 quadrillion ways to spell this word using different variations.

Trick nine: Image tricks

If you receive a spam email with an image in it, by sending it to the "junk" box you expect that your spam filter will stop the same message from reaching you again. But spammers get around this by making small, unnoticeable changes to the message or image ? changing its size by one or two percent, changing the background colour, and making small adjustments to the layout.

Trick ten: Social engineering

Spammers play on our social relationships and expectations to make the email seem more legitimate ? whether it is using the latest news headlines in the subject line to arouse our interest, or in the case of phishing emails, pretending to be a trustworthy source such as a bank to obtain account details.

They also send messages with subject lines such as "check this out" and a PDF attachment containing the spam message ? in this case, most people will not immediately think it is spam.

The solution?

There is no singular technology capable of blocking all spam ? as soon as a technology proves to be efficient, as we have seen above, spammers work out a way to get around it.

Currently, the best solution is using multiple anti-spam techniques together, which include both reputation analysis and content analysis. Reputation analysis should analyse not only the Sender IP address and content, but the links/URLs, images, attachments, the email structure and more.

Effective content analysis techniques can include Bayesian spam filtering (a method whereby an email's probability of being spam is determined)), lexigraphical distancing (checking for variations on spam words), and image inference analysis (whereby core features of an image that a spammer cannot manipulate are extracted to help determine if an e-mail is spam), as well as simpler checks such as block/allow lists and SPF checks, which combine to work out the true intent of e-mail messages.