Although Linux holds only a small market share, Linux computers appear to send a disproportionate amount of spam compared to other operating systems, according to new research from Symantec's MessageLabs messaging security division.

Symantec looked at spam from November 2009 through March and broke down what kind of operating system is on the computer that sent the spam. Analysts do that by a method called passive fingerprinting, which involves analyzing the network traffic of a remote host, which reveals that host's operating system.

Since Windows holds more than 90% of the market, the lion's share of spam still comes from Windows machines, said Paul Wood, a MessageLabs intelligence analyst with Symantec.

Symantec found that 92.65% of spam came from Windows PCs, with 2.22% coming from other operating systems and nearly none from Apple computers.

But 5.14% of spam came from Linux machines, which is unusual since Linux comprises about 1.03% of the operating system market, according to statistics quoted by Symantec in its latest MessageLabs Intelligence report for April.

Full story: Computerworld