Details of the momentous Sun-Microsoft deal signed in April have started to raise eyebrows in the open source world.

As part of its SEC filings, Sun revealed this week that under the deal, users of its Open Office software would be exempt from Microsoft's legal claws. But from 1 April 2004, all non-Sun users of the open-source software suite will not be.

What this says about Sun's approach toward the open-source movement is already being hotly debated. It has however also demonstrated Microsoft's typical two-faced approach to business. Having reached agreement to leave the way open to sue users of Open Office, this week it was telling the Open Office community it wanted to work with it, prior to its exhibit at an Open Office conference.

The Sun-MIcrosoft agreement says Microsoft can seek damages from Open Office users or distributors for any copy of Open Office installed after 1 April 2004. However, users of Sun's commercial distribution of Open Office, called StarOffice are protected from legal liabilities.

Open Office includes a word processor, spreadsheet and presentation software based on technology Sun acquired in its 1999 purchase of Germany's Star Division. Sun released the code under an open-source license in 2000.

While the agreement effectively safeguards a large group of Open Office users from Microsoft, it leaves new users vulnerable to potential legal action, said Richard Donovan, head of the anti-trust practice at Kelley Drye and Warren, who has followed the agreement. "From now on, you're on notice that if you're still putting Open Office out there, Microsoft is reserving the right to go after you," he said.

The fact that Sun has granted Microsoft the right to seek damages for Open Office after the 1 April date may indicate a weakening in Sun's support for the open source project, Donovan said. Agreeing to the clause would "only make sense if Sun had decided as a corporate strategy that they did not intend to pursue Open Office very vigorously afterwards," he said.

Sun's Castronovo disagreed with Donovan's assessment, saying that Sun's support for Open Office was "as strong as ever" and adding that Microsoft has always had the right to sue Open Office users. "That existed before, so nothing changed in that respect, he said. "Open source software is typically provided without warranty and liability coverage. Open Office is no different."

Open Office developers were somewhat confused by the "legalese" language in the clause, said Louis Suárez-Potts, a senior community development manager with CollabNet, who works on the Open Office project. But Sun's level of support for the project has not changed since the April announcement, he said. "I don't see this special chumminess [between Sun and Microsoft] as affecting our work," he said.

But one open source advocate was troubled by the clause. "It's ominous, because it means that Microsoft is holding open their right to sue end users of Open Office for patent infringement. And Sun is protecting itself by exempting StarOffice from exposure," said Pamela Jones, editor of the website, which covers legal issues relating to Linux and open source software.

"It raises questions about Sun's motives in agreeing to such a deal, but it really shines the spotlight on what Microsoft thought was important to exempt from the Sun-Microsoft patent truce," she said.

The contract clause may have been necessary because of Sun's intimate relationship with the Open Office project, analysts say. Sun engineers are the major contributors to Open Office and the company retains the copyright to all software that is contributed to the project.

Because of this tight relationship, Microsoft may have felt it necessary to remove any ambiguity about whether or not Open Office users are indemnified by the Sun-Microsoft agreement, said Matt Rosoff, analyst with Directions on Microsoft. "They wanted to make it clear that just because Sun and Microsoft have a cross-licensing agreement, that doesn't mean that Sun has the right to turn that indemnification over to an open source organisation," he said.

Ironically, the contract clause has come to light just as Microsoft is beginning to make overtures toward the Open Office development community. Microsoft's German subsidiary, Microsoft Germany, plans to exhibit at the Open Office Conference 2004 being held in Berlin next week.

Though Microsoft offers XML support with its Microsoft Office 2003 software, the company has been criticised by Open Office developers for its refusal to participate in an OASIS-led effort to develop a standard file format for productivity applications.

Microsoft decided to participate in the conference to learn about Open Office and "take an active part in the dialogue and to discuss important topics related to open standards," said Sandra Schwan, a Microsoft spokeswoman, via e-mail. "This conference is not about selling products," she said.