But John Andrews, president of market research firm Evans Data Corp. in Santa Cruz, Calif., said that Linux is slowly becoming a bigger target for attackers. "Windows was the only game in town, but now Linux is offering a more tempting prize," he said.

In a survey of 450 Linux software developers conducted by Evans Data, just under 11% of the respondents said they had found viruses on their systems. The results, which were released earlier this month, show that more than a third of the affected users reported that they had three or more infections. Those are the highest totals ever reported in the twice-yearly survey.

Earlier this month, a cross-platform virus emerged that could theoretically infect both Windows and Linux systems. Johannes Ullrich, chief research officer at the SANS Institute in Bethesda, Md., said that such proof-of-concept code has traditionally presaged the development of actual malware. "I think we'll see an increase in virus activity as Linux becomes more mainstream," he added.

Novell and Red Hat Inc. both say they have enhanced the end-user access controls in their Linux distributions using their Security Enhanced Linux and AppArmor technologies, respectively.

Some Linux users are starting to implement more safety measures. Ritz Camera Centers Inc. , which is upgrading more than 4,000 point-of-sale terminals in stores nationwide to run Novell Linux Desktop, is taking pains to ensure that the machines are isolated from the Internet, according to Bob O'Hern, senior vice president of information systems at the Beltsville, Md.-based retailer.