Image spam increases 200 per cent over last five months 15 November, 2006 By Chris Talbot

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A year ago, image spam consisted of approximately two per cent of the total amount of spam moving through cyberspace, but the amount of image spam has skyrocketed over the last four or five months, said Paul Judge, CTO of Secure Computing. Image spam now accounts for 30 per cent of all spam on the Internet.

"The reason is spammers have found a hole in the system. They've found a weakness and are working diligently to exploit it," Judge said.

Since traditional anti-spam technologies look at the text in an e-mail and judge whether it's spam or not based on the filtering of that text, many anti-spam products are not catching image-based spam. The text is an image, so they're missing it, Judge said.

"Many systems in the world have a problem catching image spam," he said.

Putting text in an image creates a blind spot for anti-spam technologies.

"The attackers have different phases and different cycles on what they spend their time exploiting. Over the years, we've seen them moving from sitting and having central servers to a more distributed architecture. One of the biggest changes over the last year was to move to zombie-based networks. Instead of using their own machines, they're using the machines of innocent people," Judge said.

Spammers have doing some heavy experimentation with image spam over the last year in the hopes of getting around anti-spam technologies and delivering their messages to end-users, Judge said. It's simply their latest attempt to slip more messages by filtering systems and squeezing the last bit of profit, he added.

"The reason that spammers have to spend all their time with these different techniques is to maximize their profit margins," Judge said.

There are two different ways to catch image spam, he said. The first way is to use optical character recognition (OCR) technology to pull text out of an image so it can be run through traditional anti-spam content filtering. The OCR approach has problems, as spammers can modify the image so that the text is readable by humans but not decipherable as text by computers, he said.

The other way is what Secure Computing uses in its anti-spam products. Secure Computing TrustedSource technology looks at the behavior patterns of senders. Based on those patterns, it categorizes senders as legitimate, suspicious or spammers. It doesn't even take the content into account, and it successfully detects over 80 per cent of spam e-mails, Judge said. Additionally, TrustedSource and similar behavior-based anti-spam technologies can stop the spam at the connection level.

"Spammers are really only getting started with image spam," Judge said. They're continuing to improve on their techniques so that as many people as possible see their messages.

The good news is spam is a dying format. Judge said he believes spam is a dying breed.

"In many battles, the loser makes these last-ditch efforts, and typically these are significant efforts, but are last-ditch efforts, if you will," he said.

It's a dying business model, he added.

"It's not as easy as it used to be," Judge concluded.