Saturday, January 15, 2011

Image Spam Trends (Part 2)

This Is Part 2 in a series of Image Spams Trends. You can check it's Part 1 - Here. The part 1 of a series describes the latest trend of Image spam but this post will be presenting new trend of image spam.

New Trends

Dynamic Zombie BotNets

Bot Nets Can be defined as
Networks of Compromised Computers which can be controlled by a single master.
The number of Nodes (also known as Zombie) of these botnets can run into millions and these machines make use of different software vulnerabilities to gain full access to the infected hosts and add it to their existing array of Zombies. Computer hackers had long been using botnets to launch DoS (Denial Of service) attacks and distribute network hacking attacks. Computer criminals had also been using botnets for money making schemes, such as stealing credit card information and spamming PPC (Pay Per Click) advertising companies. Seeing huge potential in botnets, spammers started financing hackers to make use of zombie machines. Hackers were able to offer services such as renting of botnets for a few minutes or hours and collections of E-Mail recipients (Spam Lists). The anti-virus industry noticed correlations between the spam industry and botnets. Not only were maleware writers allowing spammers to make use of their creations, but they were writing malicious code to specificially suit their needs. An unholy alliance had been created.

Most anti-spam vendors had added Bayesian filtering to their arsenal of spam blocking methods. The fight between spam and anti-spam looked like it was taking a positive turn. Thhis time the spam started looking more graphic in nature. Spammers began making use of images to bypass text-based content filtering, simply by no longer using any text content. By making use of Image spam, spammers were attacking the defenses of most antispam solutions, while the images displayed text messages to the end users, the antispam software was only able to see pixels. Some email anti spam software decided to go with OCR (Optical Character Recognition) to turn the images into text that the software could then use. However, spammers took their images to next level. In an approach usually applied to CAPTCHA (antispam solution used on web forms/forums), they started fuzzing (including noise and distortions) images to make it even harder for the machine to recognize text. Although it is possible for the machine to read this text, the process is very CPU intensive, especially when it is handling multitudes of images every few seconds.
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