The Software Freedom Law Center (SFLC) has warned that promises made by Microsoft over its Office Open XML (OOXML) document formats could leave open source software developers at risk of legal action.

The SFLC found a number of shortcomings in Microsoft’s Open Specification Promise (OSP).

But the SFLC said that the OSP lacks watertight promise for developers and said: "the OSP provides no assurance to GPL developers and that it is unsafe to rely upon the OSP for any free software implementation, whether under the GPL(General Public License) or another free software license.".

The OSP small print reveals limits to Microsoft’s specifications with patent protections that only apply to current versions, but provides no provision for future versions, which weakens the firm’s claim that its promise was "irrevocable", said the SFLC.

The team also cautioned that software developers who write Microsoft-derived code could be limited in how that code, such as the OOXML specification, is used.

“The OSP doesn’t permit free software implementation: it permits implementation under free software licenses so long as the resulting code isn’t used freely,” said the SFLC.

Unsurprisingly, the team recommends against OOXML being adopted by the ISO as an international standard.

Meanwhile, ISO members from 33 countries have until 29 March to change their minds and give Microsoft's OOXML their blessing.

Last autumn the majority voted no to adopting it as an international standard file format. ®

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