Spam, often linked to phishing attacks or fraud, now constitutes 92 percent of all e-mail, according to McAfee's Threat Reports Second Quarter 2009. Meanwhile, another anti-spam firm, MX Logic, sees that figure as even higher: a whopping 94.6 percent of all email sent.

The McAfee report states, "June produced the highest amount of spam we have ever seen, beating the previous high month, October 2008, by more than 20 percent."

Both security firms see "pharmaceutical spam," at almost 90 percent of all spam, as the single largest type of spam in terms of content, with one in particular, known as Canadian Pharmacy, the undisputed dominant force.

Criminals sending spam rely on hijacked "zombie" machines that have been taken over by malware, and the number of zombies around the world is said to be rising by an estimated 150,000 every day. "In the US alone, there are 2.1 million new zombies, up 33 percent from the last period," said the McAfee report. McAfee estimates there are a total 14 million computers "enslaved by cybercriminal botnets"

Botnets are elaborate command-and-control systems operated by botmasters to remotely control compromised computers, and they tend to be specialised for various tasks such as spam distribution, stealing identity and financial data, selling fake anti-virus software or click fraud.

In both the McAfee and MX Logic reports, the United States is seen as the top country for spam-producing volumes. Other countries cited as significant sources of spam volume are Brazil, China, Russia, Poland and India.