Google on Friday said it was buying "Web 2.0" start-up Writely, an online word processor, for an undisclosed sum.

The move might be seen by Microsoft - whose Word program is the dominant application in word processing - as a threat to its market share.

Google has challenged Microsoft in areas including search technology andemail.

Google and other internet companies such as Yahoo have been focusing on making applications, commonly run from a computer's hard drive, available remotely over the web.

Web 2.0 is the name being given to a wave of web services that offer more interactivity in the browser and "social software" such as photo-sharing and public tagging of web pages.

Writely allows users to compose and print text from inside a web browser, as well as collaborate with other users on a document.

Google revealed its acquisition in an entry in its official blog by Writely co-founder Jen Mazzon. "For the last five months, I've been part of a Silicon Valley start-up called Upstartle, which makes Writely," she wrote. "As of Monday, I'm happy to say that I and the rest of the Writely team are now part of Google."

Writely is in a developing "beta" stage, like many of Google's products, and is "far from perfect", according to Ms Mazzon.

But it will be expected to join a suite of applications being made available by Google through the browser. They include the Gmail email service and an online calendar.

Bloggers on Thursday speculated that Google would next be looking at browser-based spreadsheet applications as it sought to mirror Microsoft's Office suite of software applications.

Yahoo has followed a similar strategy of buying up Web 2.0 companies to fill gaps in its online offering and strengthen its services.