The volume of spam messages laden with malicious links or attachments is increasing, according to the latest figures.

Symantec's monthly State of Spam report claims that malware-laden messages are far more common than in the first half of the year. The security firm estimates that 1.2 per cent of all email messages sent contains a malicious payload.

Overall, Symantec found that spam comprises some 78 per cent of global email messages.

While attached .zip and .rar archives were the most popular method for spreading malware, researchers also found that embedding attack code within the source code of the message itself is becoming popular.

"The increase began in May 2008 and continues to the present," the company said in the report. "During this period, there has also been an increase in email messages carrying malware payloads, not just links to malicious code."

The majority of the malicious payloads were generic Trojan, downloader and information stealing applications.

Trojan attacks comprised 13.4 per cent of malware detections, while downloads and 'info-stealers' logged 11.8 and 11.1 per cent respectively.

The Pandex Trojan was the most popular single piece of spammed malware, followed by W32.IRCBot and the Goldun Trojan.

China was the most popular origin for malicious spam messages, followed by the Republic of Korea, the US, Thailand and Vietnam.