ASCII Art Spam Strikes Back

Spammers are always looking for techniques that can beat the spam filters. We have seen various techniques for spamming–like obfuscating words, embedding text in images, spoofing urls, abusing social networking sites, and many other techniques for spam to avoid getting caught.

One of these techniques is ASCII art, an artful way of representing an image using text characters. These representations first appeared long ago to overcome the limitations of computers for displaying graphics.

Example:

______    _____   ______    _       _____    _____     ___
| ___ \  |  ___|  | ___ \  | |     |_   _|  /  __ \   / _ \
| |_/ /  | |__    | |_/ /  | |       | |    | /  \/  / /_\ \
|    /   |  __|   |  __/   | |       | |    | |      |  _  |
| |\ \   | |___   | |      | |____  _| |_   | \__/\  | | | |
\_| \_|  \____/   \_|      \_____/  \___/    \____/  \_| |_/

The clever thing is that each line has some random characters with _ and | characters, which do not resemble any part of the word replica. If we take the entire picture into consideration, though, our eyes can read it as a word. The spammers try to take advantage of this to pass through spam filters and deliver their intended message.

Not only are the words represented in this manner but even URLs can be displayed in this way to avoid the blacklisting of the domains.

ASCII art spam is not limited to only nonword characters. It can be numbers, alphabets, and combinations of both, which can make things even worse for certain spam filters:

dP""b8  88     db     88     88  dP"Y8
dP      88    dPYb    88     88 `bo
Yb      88   dP__Yb   88     88   `Y8b
 YboodP 88  dP""""Yb  88ood8 88  8bodP'

In the email above we can see that the spammer is advertising a pharmacy product without using the respective words, yet still successfully conveys the message.

We saw this spam technique some time back, but it had died off. Recently, however, we have seen an increase. McAfee customers are protected from this type of spamming technique.