SonicWALL's Smartlab network reports: "Image spam, which attempts to bypass mail filters by using graphics rather than text, rose nearly 500 per cent in 2006."

Image spam, today, accounts for 35 per cent of messages and 70 per cent of bandwidth taken by spam. Zombie activity (name given to computers remote-controlled by hackers), says a security report, accounts for 85 per cent of the spam circulating on the Internet.

According to a report by CommTouch Software, multiwave image spam outbreaks brought spam bloat to 1.7 billion MB per day. Popular websites like eBay and PayPal were the prime targets for fraud, as names were used in 50 per cent of all phishing attempts.

The study also states: "The number of zombie machines went up to 8 million hosts globally on a given day and a direct result was that the spam volume rose 30 per cent in 2006."

Joy Ghosh, managing director (APAC), IronPort, feels while image spam has been around for some time, it is only recently that attackers have been making use of it to more effectively bypass spam filters.

"Spammers are getting cleverer in how they send and code the images," he says. Ghosh explains why people felt the flood of spam more intensively in 2006.

"Since many anti-spam technologies have not been able to keep up with the spammers' ever-growing bag of tricks, we saw more spam in our inboxes," he elaborates. Of all the email that one receives in the inbox, spam range is pegged around 45-98 per cent of all Internet messages.

The threat posed by image spam, feel experts, is not only at par with other types of text-based spam but can also be an additional drain on an enterprise's bandwidth and storage resources, since images take up more space on the Internet pipeline and mail servers.

Gleb Budman, senior director of Email Security, SonicWALL, foresees image spam to exacerbate the administration requirements around spam.

"By its nature, image spam will get only bigger and take longer to process, so there will be some pressure on IT and the messaging infrastructure to deal with increase of data," he predicts.

"You do not want those messages to undermine the availability of data in your enterprise," adds Niraj Kaushik, country manager, Trend Micro (India and SAARC).  "Yes, this could generate a few grumpy users, but at least the mail servers will be up and running," he says.

The experts suggest that companies pay attention to the volume of incoming messages with image attachments, and if a significant portion of those messages are not being blocked, it may be wise to restrict the delivery of certain image-based messages.

This variety of spam contains images spouting everything from stock scams to Viagra, and its volume has more than doubled since last year, according to an analysis by IronPort.

Organisations and home users using comprehensive anti-spam products - those that focus on both the content and origin of messages � have little to worry about, other than to make sure that they use the latest version of their vendor's products and receive regular updates.