Microsoft still hopes to strike a Linux pact with Red Hat, similar to its deals with Novell, Xandros and Linspire, according to strategy leaders.

"We'd love to do the same deal with Red Hat," said Tom Robertson, general manager of corporate interoperability and standards at Microsoft. "We're always open to talking with them."

That sentiment has not so far been echoed by Red Hat's. The company has said it's not interested in a deal. Red Hat spokeswoman Leigh Day said that is still the case.

"We continue to believe that open source and the innovation it represents should not be subject to an unsubstantiated tax that lacks transparency," she said.

Still, some wonder - as Microsoft lines up the other Linux ducks in a neat little row - if Red Hat might be next, and rumours suggest a pact might be imminent. Microsoft's latest Linux deal came last Thursday with Linspire, a deal that would shield the company's customers from Microsoft patent-infringement claims.

The deal follows one struck by Microsoft and Linux distributor Xandros, and a high-profile and financially significant deal with Novell late last year.

Microsoft has said it is seeking these partnerships for a couple of reasons. The one Robertson is most interested in is interoperability, as he - along with Jean Paoli, general manager, interoperability and XML architecture - is in charge of Microsoft's 18-month company-wide strategy in this area.

Robertson said Microsoft customers have demanded the company address interoperability issues with other companies' software, including open source, and that IP in those products is a concern for them. "If you look across the industry, you see companies working together to address IP on behalf of their customer base," he said.

Microsoft has publicly said that Linux and other open-source software violates 235 of the company's patents. But rather than suing to settle these IP claims, Microsoft is striking individual deals, Robertson said. However, much has been made of the fact that the company has not publicly disclosed any of the patents it claims open-source software is violating.

Robertson would not address why Microsoft will not show its patents, and stopped short of claiming the deals with Novell, Linspire and Xandros prove those companies are indeed violating Microsoft IP. None of the Linux companies will say so, either, and Novell in fact has vehemently denied infringement. This discrepancy is one reason some feel Red Hat will never sign up for an indemnification deal with Microsoft.

The size and business viability of the companies that have signed on is another. Novell was flagging when its deal was struck - and the company has continued to wane even since - and some familiar with how it happened said it was a bailout to save the vendor from being split up and sold piecemeal. Indeed, Novell's US Securities and Exchange Commission filing about the deal revealed that Novell got $348 million up front from Microsoft for patent cooperation and Linux coupons, while only having to shell out $40 million to Microsoft in return.

Though Microsoft will not comment on the financial terms of deals with Xandros and Linspire, those familiar with the agreements said those companies also received financial compensation from Microsoft. This begs the question that if interoperability and protecting customers are Microsoft's ultimate goals for the deals, as Robertson said, why is the company so interested in Linux companies that ultimately don't affect that many customers?

Many - particularly those in the Linux camp - suspect Microsoft is trying to make it appear that open-source distributors are violating Microsoft IP to vilify them in an effort to dissuade customers from using Linux and other open-source technologies.

Bruce Perens, a long-time Linux and open-source advocate, said Microsoft is giving Linux companies that are on the edge of going out of business money to create the illusion that Linux vendors are stealing its IP. Perens is a vice president at SourceLabs, a company that provides testing, management and certification of open-source software to users.

"Here is Microsoft out collecting the losers in the Linux business and paying them money so they can ... paint open-source as music pirates out there using Microsoft technology without a licence," he said. "I think they're out to scare people."

Even if this is the case, it takes two to tango, and it's important to note that companies such as Novell, Linspire and Xandros benefit in various ways from their deals with Microsoft. Aside from any financial compensation, the companies also gain access to Microsoft technology that would make their own Linux products more viable in the marketplace, analysts said.

"These companies want the deals with Microsoft because it will make the products more attractive and more compatible with the Windows world," said Michael Silver, an analyst with Gartner. "It's pretty clear that there is definitely value for these companies."