Addicts of Scrabulous, an online word game played by millions of office workers on Facebook, may soon have to go cold turkey because of a looming copyright battle with the owners of Scrabble.

The two entrepreneurs behind Scrabulous, who are making more than $25,000 a month from their widely downloaded application, face a legal challenge from the two toy companies that own the rights to the board game.

Hasbro owns the intellectual property rights to Scrabble in the US and Canada, while JW JW Spear & Sons, a UK-based subsidiary of Mattel, holds them in the rest of the world.

Launched in July 2006 by Rajat and Jayant Agarwalla, brothers in their 20s from Calcutta, Scrabulous has become one of the most popular games played by Facebook members and boasts nearly 600,000 daily active users.

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While there are many similar online word games, including Literati, they arguably borrow less obviously from the Scrabble name and format than Scrabulous, a factor that may be important in determining the extent of any copyright infringement.

Comments written on a blog on the Scrabulous website give a hint of how it may be eating into revenues that would otherwise have gone to the companies that own the Scrabble brand.

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"I have been having a lot of fun playing and chatting," wrote Cat, a user. "I was going to purchase the dvd scrabble but now i decided not. This is much more fun playing."

Mattel UK said: "Letters have been sent to Facebook in the US regarding the Scrabulous application . . . Mattel values its intellectual property and actively protects its brands and trademarks."

Rajat Agarwalla told the Financial Times that he "could not comment on legal affairs right now".

He confirmed that the group made "over $25,000 a month", principally from selling advertising space on the application.

A disclaimer on the Scrabulous website says: "Scrabulous is not a part, subsidiary, or venture of Hasbro or Mattel, and is not connected to them in any way whatsoever.

"We hope this will encourage people to purchase the official board game and make sure that Scrabulous remains something that our children still come into contact with despite these days of electronic games culture."

The brothers originally launched their online game as Bingobinge in August 2005, but renamed it Scrabulous the following July.

The game became a hit only after it was put up on Facebook in June 2007.

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