In what amounts to a case of "The Empire Strikes Back," the software giant in recent weeks has deployed a team of engineers and marketers to keep tabs on Linux, the fast-growing, free operating system that is making waves in the computer world. The group in Redmond, Washington., is small -- fewer than 10 members -- but it has an important mission: to counter a cultish software movement that has evolved from a mere annoyance to a real threat. Microsoft's team is already moving to convince potential corporate users that Linux is not ready for prime time. The Linux effort mirrors Microsoft's response to other marketplace threats, such as Sun's Java programming language. While pointing out potential problems with Linux, the group continues to bone up on the software in an effort to understand its appeal. "Getting inside the head of our competitors is one of our best practices here at Microsoft," says Jim Ewel, a director of marketing in the company's Windows 2000 organisation, who is in charge of the effort. But Linux isn't a typical target. It is the brainchild of Linus Torvalds, a 29-year-old Finn who helps co-ordinate a global network of volunteers who refine and test the program. Linux' open development scheme and robustness have long appealed to technical computer users. In recent months, though, Linux has been embraced by many big computer companies, and competes with Microsoft's Windows NT operating system on midsize machines called servers. The battle would seem a hopeless mismatch. Microsoft is a tightly focused organisation that does most development work behind closed doors on one corporate campus. With Linux, programmers in several countries plan, discuss and argue about technical changes in the open, usually in Internet news groups. Microsoft directly controls every facet of Windows; Mr. Torvalds takes a far more laissez faire approach to many parts of the operating system, like its user interface, which he leaves for others to handle. What's more, while Microsoft is one of the most valuable companies on earth, Mr. Torvalds doesn't even have a secretary. Recently, when he came back to his office at a Silicon Valley chip company from a two-week family vacation, he had 2,000 e-mail messages in his in-box. But Mr. Torvalds says he isn't troubled by the disparity. "Microsoft has the advantage of being big and rich, but they have the disadvantage of not being very likeable or trusted," he says. "I think it will be OK." In a way, Linux has done Microsoft a favor, allowing the company to argue in the current antitrust trial that it faces credible competitors. But the competition isn't only in Microsoft's legal briefs. International Data Corp., of Framingham, Mass., says that Linux's share of unit sales of server operating systems rose to 17% last year from 7% in 1997, the fastest growth rate in the industry. By contrast, Windows NT's share was essentially flat, at about 36%. Numbers like those have helped undermine the perception -- common just last year -- of Windows NT's being unstoppable, especially in the tightly contested server market. "When a competitor reaches a certain threshold, Microsoft starts to pay attention," says Tony Iams, an analyst with D.H. Brown, a Port Chester, N.Y., consulting group. Linux has clearly reached that point." The situation is not lost on Jim Allchin, Microsoft's senior vice president in charge of operating systems. Where Linux once received little serious attention, it is now being subjected to the same tough performance analysis as rival products from major corporations. "I have now upped the focus on it," Mr. Allchin says. "I've got the performance team prepared to benchmark it every which way." The performance of Linux is one of the themes of the emerging Microsoft response to the operating system. The company had been badly embarrassed about a speed test run early this year by a trade magazine showing that Linux was more than 50% faster than NT on a typical entry-level desktop computer. Microsoft argued that a better test would be on a beefier machine, the sort used to run a small business, and commissioned Mindcraft Inc., a benchmarking outfit in the U.S., to run one. Mindcraft reported back that NT was 3.7 times as fast as Linux on a server with four microprocessors. That report brought howls from Linux users, who complained that the Mindcraft testers had tweaked NT to get the best performance, but had run Linux unmodified. The study also led to some snippy e-mails between Mr. Torvalds and Microsoft's Mr. Ewel. "Shame on you," wrote Mr. Torvalds to Mr. Ewel at one point. The Microsoft executive, when accused of rigging the test, responded by characterising Mr. Torvalds's argument as "bulls---." Mindcraft reran the test, this time with input from Mr. Torvalds and others. Linux did better the second time. But even Linux boosters admit that their operating system can't yet keep up with NT on bigger systems. For example, Jeremy Allison, an employee of Silicon Graphics Inc. who works on a software package called Samba that's often used with Linux, says his tests show that NT is 50% faster than Linux on a four-microprocessor machine communicating with desktop machines running Windows 95. Mr. Allison says, though, that Linux does better than NT when Linux is serving desktop machines running Windows NT. He also says that even if Linux lost some benchmarks to Windows, it is still a far more stable piece of software. Mr. Ewel rejects that claim. "NT runs some very reliable Internet sites," he says. "You wouldn't see that kind of market share if we were as unreliable as" rivals have said. Microsoft remarks about Linux have become more pointed since August, when an internal memo suggested that it had reached a quality comparable to commercial software. Chairman Bill Gates, for example, recently characterised Linux as useful only for specialised computers. In another facet of its Linux campaign, Microsoft recently posted a Windows vs. Linux comparison page on its Web page, listing what it says are the advantages of its product and shortcomings of its rival. Overall, Microsoft says Windows is more reliable and secure than Linux, and runs better on bigger machines. But Linux will be a moving target -- Thursday, for instance, Silicon Graphics said it was making available its highly-praised computer file system for use with Linux. There is no debate on one point -- that the conflicting claims about Linux and Windows NT are just beginning. Mr. Torvalds says that Linux developers will now pay more attention to the benchmarking tests that Linux currently scores badly on. Mr. Ewel agrees the argument won't be settled soon. "This is a marathon, not a sprint," he says. Take me to the Linux Lounge