Image-based spam blamed for spam hike

Spam levels have increased by up to 60 percent

Researchers and IT managers are confirming security vendors' claims that spam levels have spiked in the past month -- some say by as much as 80 percent -- and show no signs decreasing.

"There are enormous amounts of spam; it's shot up like crazy since the beginning of October," says John Levine, president of consulting firm Taughannock Networks and co-chair of the Internet Research Task Force's Anti-Spam Research Group, which operates a number of e-mail addresses that aren't filtered for spam. "Earlier this year I was seeing about 50,000 spam messages a day, now I'm seeing 100,000."

Levine's assumption is this spike in spam levels is a result of a new generation of viruses and zombies that can infect PCs more quickly and are harder to get rid of. In its October report, messaging security vendor MessageLabs says the spike is largely due to two Trojan programs, Warezov and SpamThru.

Others say a new breed of spam messages called image spam -- messages with text embedded in an image file that evade spam filters, which can't recognize the words inside the image -- is responsible.

At North Shore-LIJ Heath System, a network of hospitals based in New York, with about 12,000 e-mail users, there's been an 80 percent increase in spam received in the last 45 days, says system architect Steve Young, and most of it is image spam.

"We got slammed with a 50 percent increase [in spam] in one day. For the past year-and-a-half none of my users ever got a spam message; in that first 48 hours [of image-spam blasts] there were 500 calls and over 1,000 complaints from users," he says.

The majority of these image spam messages are so-called pump and dump scams, where spammers purchase a penny stock, promote it through e-mail, then sell it at a profit. Most appear to come from Europe, says Levine.

After receiving so many calls from his users Levine called BorderWare, his e-mail security vendor, to ask for help. The company enrolled him in a beta program for its new technology designed to block image spam, which Levine says is working. "We blocked 7,000 image spam messages in the first day" of trialing the new technology.

What's made image spam so vexing is that spammers have learned to represent words in an image that are recognizable to the human eye because of the way people recognize images that a computer can't understand, says Andrew Graydon, CTO of BorderWare.

"They're banking on eye recognition, and so many of the solutions out there only deal with text analysis," says Graydon. The company's new technology, set to be unveiled next week, analyzes image spam and comes up with a characterization of the message that tracks 30 different pieces of information about it that mimic the way people visualize.

Of course, as vendors come up with new techniques, spammers do, too. Image spam began popping up a few months ago, and security vendors responded with products that create a "fingerprint" of the message and match that against new incoming messages. Then spammers began randomizing image spam so that each message was slightly different from the last, therefore evading fingerprinting technology.

"On a scale of one to 10, I would rate image spam as an 8" in terms of how troublesome it is, says Paul Judge, CTO of Secure Computing. "This is because spammers have leapfrogged from hiding text within other text to now moving it to a place that is unreachable by most antispam systems."

Secure Computing is touting its TrustedSource Message Reputation fingerprints, which take a snapshot of a message identified as spam and then assigns a correlating reputation score to it. The company is adding ImagePrinting technology to this service that creates fingerprints specifically for images.

While spammers can circumvent fingerprinting by changing even one pixel in the image, Judge says Secure Computing's ImagePrinting technology performs image normalization "to ignore variations and focus on reoccurring parts."

Tumbleweed on Tuesday introduced its Adaptive Image Filtering technology designed to block image spam by using an image-processing technique called wavelet transform, which reduces an image to a mathematical formula that represents the message but still allows for variation, according to company officials. With the addition of this new filtering technology to Tumbleweed's e-mail security appliances and software, the products can catch image spam that has been randomized in order to circumvent spam filters, they say.

The company has already analyzed thousands of image spam messages and continues to build its pattern-matching database to check incoming e-mail messages against, officials say.

Whether or not antispam products can catch this new variant of spam, this huge increase in unwanted e-mail levels is concerning because it necessitates more bandwidth and computing power for anyone running an e-mail system, says Levine.

"Spam is huge tax on e-mail, and the tax just doubled," he says.

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Cara Garretson

Network World

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