"Rustock allows spammers to send out image spam, which is more difficult for traditional antispam software to accurately identify.

"Finally, 80.2 per cent of Web viruses intercepted were from uncategorized sites suggesting that they were being used for domain kiting and other disreputable purposes to host phishing and spam sites."

The ISS 2006 security statistics report identified advances in image spam technology, operating system holes, and an increased hacker focus on Web browser vulnerabilities as the top concerns for 2007.

The ISS X Force research and development team has predicted new forms of image spam will be pervasive throughout 2007.

It will be specifically designed to evade capture, however, IBM ISS director of security strategy, Gunter Ollmann, said the good news is the drop in high-impact vulnerabilities.