Which operating system, Linux or Windows, is cheaper, more secure, and lower risk? Countless hours have been spent debating the question, and last week, Microsoft CEO Steve Ballmer sparked the argument again. In a letter E-mailed to customers, Ballmer contended that a growing body of data proves that Windows beats its open-source competitor on all three fronts.

"It's pretty clear that the facts show that Windows provides a lower total cost of ownership than Linux, the number of security vulnerabilities is lower on Windows, and Windows' responsiveness on security is better than Linux," Ballmer wrote. "And Microsoft provides uncapped IP [intellectual-property] indem- nification of their products, while no such comprehensive offering is available for Linux or open source." (For more on Microsoft's intellectual-property and indemnification strategy, see story, Microsoft Deepens Indemnity)

Ballmer also touted Windows' strengths as a platform for companies migrating enterprise-resource-planning applications from Unix systems, and he highlighted a handful of companies, Equifax Inc. among them, that have opted for Windows over Linux. The position paper comes with Windows Server 2003 sales continuing to rise at a healthy rate but with Linux growing even faster. Ballmer would like to change some minds.

Ballmer's Windows-beats-Linux missive--only his second E-mail to customers this year--is a predictably one-sided argument even to analysts whose research is used to bolster his point of view. "It's the world according to Microsoft," says Yankee Group analyst Laura DiDio, author of a report cited by Ballmer that compares the costs of Windows, Linux, and Unix.

The truth is likely somewhere in the middle, with Windows outperforming in some scenarios and Linux in others. One of the Yankee Group case studies involves a New York law firm that estimated the cost of switching from Windows to Linux would be more than three times higher than sticking with Windows, driven by the expense of reprogramming applications and administering a new software environment. Yet, the IT research and advisory firm also found that Linux offers "compelling cost savings" for some other companies.

Ballmer may have invited the sharpest reaction for his bold assertions about Windows' security advantages. Only two weeks earlier Microsoft issued patches for an eye-popping 21 vulnerabilities in Windows, Exchange, and Office. "The reality is that the financial impact to the economy and to customers of the malicious attacks on Microsoft products has run into the billions," competitor Novell wrote in a point-by-point rebuttal to Ballmer's correspondence.

A March report by Forrester Research found that Microsoft issued patches more quickly than Linux distributors once a software vulnerability was publicly disclosed, and Microsoft had fewer flaws to fix than Linux versions. On the other hand, Microsoft had the greatest percentage of vulnerabilities ranked "high severity," a point that Ballmer ignored. And Forrester's data is more than a year old.

It's easy enough to find similar soft spots in Microsoft's "Get The Facts" marketing campaign, from which Ballmer drew much of his ammo. A Microsoft-sponsored study by BearingPoint, for example, found licensing and support costs of Windows Server 2003 only to be "comparable" to Novell's SuSE Linux 8 and Red Hat Inc.'s Enterprise Linux 3, with Windows being less expensive only in some cases.

Ballmer emphasized the independent nature of the data Microsoft gathered. Perhaps that was to head off questions about the objectivity of the reports bolstering his position. Microsoft occasionally has paid fees to firms such as Meta Group and BearingPoint to commission reports documenting Windows' advantages, and it has even reviewed some reports prior to publication. Even when it doesn't commission reports, Microsoft sometimes pays licensing fees to redistribute unsponsored analysis it deems favorable.

How did Ballmer's spiel play among business-technology executives? Scott Bess, IT director with Goodwill Industries of Central Indiana, thinks Ballmer got it right but says, "Ours is a little more practical stance." The nonprofit organization uses Microsoft software to support operations that span 27 retail locations, two schools, and a manufacturing plant. Its IT staff dabbles with Linux but has no plans to switch platforms. Bess says he doesn't believe Linux would be cheaper or more secure than the Windows infrastructure now in place. Besides, he doesn't want to focus resources on operating systems, he says. "I want to support the applications we write. To us, that adds better value to the business."

Burlington Coat Factory Warehouse Corp. has been using Linux and Apache for five years. The apparel company uses Windows sparingly, mostly on certain retail systems. CIO Mike Prince says he hasn't seen any evidence that Windows is more secure than Linux. "I don't think we've ever had a virus on Linux, and those systems will run for six months without needing to be rebooted," he says.

IT shops that are predisposed to running Windows, and that have invested in it, are less likely to see cost benefits from migrating to Linux, Prince admits. "But on a clean playing field, I can't see how Linux would be more expensive than Windows," he says.

The executive behind Microsoft's anti-Linux strategy, general manager Martin Taylor, says Microsoft understands its open-source competitor better than it did a year ago. And that knowledge doesn't just come from hard competition out in the marketplace. Microsoft is getting hands-on experience by running major Linux distributions and other open-source software in a computer lab on its Redmond, Wash., campus. Says Taylor, "I feel we've got great line of sight to where we know we can win."

--With Larry Greenemeier