Microsoft come out in favour of ODF, the document file format used widely in open-source alternatives to Microsoft Office - to allow "choice" in business standards.

The company has backed the inclusion of ODF in a list of standards maintained by The American National Standards Institute (ANSI) - as well as backing Microsoft's own OpenXML format, used in Office 2007, for inclusion in the list.

The company said it supports Open Document Format (ODF) for XML because businesses want choice and interoperability for software they deploy. ANSI recommends business best practices, standards and guidelines to a range of industries in the US.

However, there may be other reasons for the move. Days ago, Microsoft slapped the open-source community with litigation threats if distributors and users do not strike deals with the vendor to pay for patents Microsoft allegedly holds for technology in Linux and other open-source software. OpenOffice.org, an open-source alternative to Office that supports ODF, contains 45 of Microsoft's patents, the company claimed in the Fortune article where it laid out its aggressive stance.

"On the one hand, Microsoft is saying 'Nice standard you've got there', while on the other hand, warning 'implement it if you dare, but only for a price'," noted Andrew Updegrove, an advocate for open technology standards and attorney with Gesmer Updegrove.

Updegrove has said that by supporting ODF as an ANSI standard, Microsoft is "making it appear it is rising above the squabble to do the right thing". Insead, he thinks the move serves as a challenge to vocal ODF supporters to support approval of Open XML as a global standard when a final vote for the draft specification comes before the International Organization for Standardization (ISO).

To its credit, Microsoft voted for ODF when it came before the ISO, while IBM cast the only negative vote for Open XML when it was up for approval by standards organisation Ecma International, Updegrove added.

Battle lines between Microsoft and ODF supporters such as IBM and Sun Microsystems have been drawn for some time, and ODF and Open XML have emerged as the key rival standards for documents. Some government agencies in the US and abroad have said they will support ODF as the standard format for documents, a decision that may require them to stop using Office in favor of OpenOffice.org, or similar ODF-supported offerings from Sun, IBM and Google.

ODF has already been approved by ISO, while Open XML will be up for an approval vote late this year.