Microsoft has revealed it will also patch Word on the Mac to comply with a federal court's ruling requiring it to remove custom XML technology from its popular word processing software.

In late December, a federal appeals court affirmed a lower court's injunction that barred Microsoft from selling Word 2007 and Word 2003 starting January 11 unless it dumped custom XML features from the software.

In May 2009, a Texas court also ordered Microsoft to pay developer i4i nearly $300m in damages, court costs and interest for allegedly violating the Canadian company's custom XML patent.

Word 2007 for Windows was first updated in 2009 with a version for computer makers, then last week with a patch aimed at end users.

According to Microsoft spokesman Kevin Kutz, Word 2003, which was also named in the injunction, must be modified because customers purchasing or licencing Word 2007 have 'downgrade' rights to the older edition.

Microsoft has also posted an update for Word 2003 for Windows on its download center.

The patch, which weighed in at 5.6MB, was similar to the earlier Word 2007 update, in that it was mandatory only "if you have been instructed to do so in a separate communication from Microsoft", read the accompany support document.

Users who bought or licensed Word 2003 or Word 2007 before January 10 do not have to apply the patches.

Although the Mac versions of Word were not specified in the injunction, Microsoft will also pull the offending technology from those editions, Kutz confirmed.

"While Office for Mac products were not accused of infringement, we are changing the product to allay any potential concerns about compliance with the injunction," Kutz said.

The patent infringement case has attracted interest because of the injunction blocking Word sales.

The injunction was originally to take effect October 10, 2009, but the appeals court suspended it while it heard Microsoft's plea.

Microsoft has not given up on the case.

Last week, it asked the Court of Appeals for the Federal Circuit to either grant a rehearing of its appeal with the same three-judge panel, or consider an en banc hearing before all the judges of the court.

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See also: Microsoft tackles locked Office 2003 files