The latest build of Office 2010 has leaked on to the web - just hours before a preview of the software is set to be unveiled.

A new version of Office 2010, build 14.0.4302.1000, has appeared on several BitTorrent tracking sites , including Mininova.org. Both the 32- and 64-bit editions leaked to file-sharing sites.

The 32-bit version showed about 30 "seeders" - the term for a computer that has a complete copy of the torrent file - and about 400 "leechers," or computers that have downloaded only part of the complete torrent. Approximately 1,200 copies of the file had been downloaded.

Office 2010 has leaked before. In May, a week after Microsoft announced that it would issue the Technical Preview this summer, an early edition showed up on BitTorrent.

Microsoft is set to kick off its Worldwide Partner Conference (WPC) today by announcing its ready to distribute Office 2010's invite-only preview, and by demonstrating Office Web - lightweight, online versions of Word, Excel, PowerPoint and OneNote.

Although Microsoft said that the Office 2010 Technical Preview will be issued to hundreds of thousands of users, it's an invitation-only prelude to a wider public beta that the company will run later this year. Microsoft has not announced a date for the beta, but expects to provide millions of copies of the suite.

Office 2010 is expected to ship sometime during the first half of next year.