The Open Source Initiative (OSI) has approved two Microsoft licences as compatible with the definition of open source.

The OSI gave the thumbs-up to the Microsoft Public Licence (MPL) and the Microsoft Reciprocal Licence (MRL), two of Microsoft's so-called "shared source" licences. They join the OSI stable alongside more widely used community licences such as the GNU General Public Licence and the Mozilla Public Licence.

"Today's approval by the OSI concludes a tremendous learning experience for Microsoft and I look forward to our continued participation in the open-source community," said Bill Hilf, Microsoft general manager of windows server marketing and platform strategy, in a statement.

Microsoft submitted licences from its Shared Source Initiative to the OSI in July. The news was generally well received by top open-source community leaders at the time, though some noted that such a move could have come a lot sooner.

The MPL and MRL are two of three licences that Microsoft offers in its Shared Source Initiative, which it has offered for about five years as a way to share source code without having to work with open-source organisations or companies. The other is the Microsoft Reference Licence, which is the most restrictive of the three and was not submitted for approval.

The MPL is the least restrictive of the Shared Source licences, allowing licensees to view, modify and redistribute the source code for either commercial or non-commercial purposes. The licence also allows licensees to alter the code they share with others as well as to charge a licensing fee. The MRL, which the company recommends for collaborative development projects, carries requirements if licensees combine their original code with MRL-licenced code. It does, however, allow for non-commercial and commercial modification and redistribution of licenced software.

Red Hat executive Michael Tiemann, who also serves as president of the OSI, said that while some in the community balked at the OSI accepting licences from a company that has not been open-source friendly, in the end, the licences spoke for themselves. "They do have two licences that went through the community process and did sustain the open-source definition," he said.

However, this does not mean the process went entirely smoothly. While Microsoft was co-operative and asked for no special treatment during the process, the OSI had to field about 400 emails from community members about the decision to let the licences go through the approval process, Tiemann said. And the OSI already is experiencing backlash from open-source proponents.

"I've received three emails in the last hour from people who say, 'To heck with the OSI, you guys are just now pawns in Microsoft's game ... you have made a deal with the devil," he said. However, Tiemann believes the OSI had a responsibility to be fair and impartial.

"What would you think of a club that would say, 'We won't take any members that come from the city of Chicago, even if two people in Chicago meet the criteria for entry?'" he posited. "We said from the outset that we would be fair and, to be honest, some people said, 'No, you don't.'"

Microsoft has shown itself to be more co-operative with the open-source community, even launching recently a new website devoted to educating the community about its initiatives in this area and to showing how its proprietary technology can work with open-source software.

At the same time, however, executives have been making bold claims about how much Microsoft intellectual property is contained in open-source software like Linux, and threatened to collect royalties. These claims are widely viewed as a way to spread fear, uncertainty and doubt among customers looking to adopt open-source software as an alternative to Microsoft products.

Tiemann said it remains to be seen if any companies other than Microsoft will license code under MPL or MRL. However, he said if Microsoft plans to embed patented technology in software licenced under an OSI-approved licence and "call it open source" - as some open-source proponents fear - they had better think twice.

"If there is some experimentation on their side to see whether or not they can produce royalty-bearing open-source code, I think they'll see that 400 messages is just the beginning," Tiemann said.