Linux-based computers are five times more likely to send spam than Windows PCs, relative to market share, according to the latest MessageLabs Intelligence Report from Symantec Hosted Services.
The firm obtained the passive fingerprinting signatures of spam email traffic for the first time in this month's report, in order to learn the type of operating system running on the infected spam-sending machines.
Paul Wood, senior analyst for Symantec Hosted Services, explained that the common perception has often been that Windows machines are responsible for the majority of spam given the high number of infections.
"We found that more than 90 per cent of spam comes from Windows machines, which is not surprising," he said.
"But if you look at Linux, it has only a one per cent market share but is responsible for more than five per cent of spam. So in a sense you're more likely to get spam from a Linux than a Windows machine."
However, Wood added that a likely explanation for these figures is much of that one per cent market share could come from Linux-based servers run by internet service providers, many of which now force clients' email traffic through these servers.
The report also found that the Cutwail botnet has been surpassed by Rustock as the largest in terms of infected PCs and volume of spam. However, overall levels of spam had "not changed an awful lot", said Wood.
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