OpenOffice.org 3.0 was downloaded 3 million times in its first week, with about 80 percent of the downloads by Windows users, an official with the group said in a blog post on Monday.

The successful introduction of the open source office suite came despite the group's download servers being temporarily overwhelmed by demand for the new software last week.

Only 221,000 downloads by Linux users were recorded, leading John McCreesh, head of marketing for OpenOffice.org, to suggest a massive undercount. McCreesh said 90 percent of Linux users traditionally receive OpenOffice.org updates straight from their Linux distribution's vendor, which would explain the relatively low Linux count.

Many non-English versions of OpenOffice.org are also distributed by alternate Web sites, and OpenOffice.org is still widely distributed via free CD-ROMs in magazines, said McCreesh.

With the undercount included, OpenOffice.org 3.0 may already be installed on up to 5 million computers worldwide, McCreesh said in a blog post.

OpenOffice.org's goal of winning 40 percent of the office software market by 2010 "doesn't seem as ambitious today as it did four years ago," said McCreesh.

Michael Croan, a senior marketing manager at Microsoft, said, "Business customers can easily see that Microsoft Office provides the productivity improvements they seek."

"Microsoft Office is well integrated, well supported and up-to-date with modern workforce requirements like collaboration, which is not always the case with open source alternatives. As a result, most customers will continue to seek the productivity improvements they can get from Office," Croan said.

Microsoft claims more than 550 million users of Microsoft Office.

OpenOffice.org's total usage, while unknown, remains small overall, despite its free price. That is due to document compatibility fears and Microsoft's aggressive, tactical discounting.

OpenOffice.org 3.0 eases some adoption concerns. It is able to open all Office-formatted files, including the latest Office Open XML (OOXML) documents (.docx, .xlsx, .pptx, etc.), but it cannot save OOXML files natively.

OpenOffice.org is also likely counting on the current corporate cost-cutting environment to help its third try at unseating Microsoft Office.

OpenOffice.org 3.0 also marks the first native Mac OS X version. Mac users accounted for 320,000 downloads of the new software in the first week.