Spam levels have spiked over the past month – some say by as much as 80 percent – with a new breed of email nuisance credited with the upsurge.

"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. "Earlier this year I was seeing about 50,000 spam messages a day; now I'm seeing 100,000."

Levine's assumption is that 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.

Others say a new type form of unsolicited email – image spam – is responsible. This threat is formed by an email with text embedded in an image file that evades spam filters, which can't recognise the words inside the image.

What's made image spam so vexing is that spammers have learned to represent words in images that are recognisable to the human eye but that a computer can't understand, according to 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, analyses image spam and comes up with a characterisation of the message that tracks 30 different pieces of information about it that mimic the way people visualise.

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 randomising 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 eight 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."

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 email security appliances and software, the products can catch image spam that has been randomised in order to circumvent spam filters, they say.

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

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

"Spam is a huge tax on email, and the tax just doubled," he says.