The move to take down one of the most popular applications on Facebook - Scrabulous - gathered momentum yesterday.

Hasbro, the toymaker which owns the rights to the Scrabble trademark in the US, announced that it was suing the two Indian brothers responsible for creating the game, which allows Facebook users to play games against one another on the internet.

Hasbro also asked Facebook to take down the game, which is played by 450,000 of its users every day.

Less than two weeks ago Hasbro said it would launch its own 'official' version of the game on the social networking site later this month - a move that was widely interpreted to mean a legal action against the unsanctioned alternative was imminent.

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The general manager for digital media and gaming at Hasbro said yesterday that the company had waited until there was a "legal" version of Scrabble on Facebook before it took action against the Scrabulous creators.

The lawsuit, filed in a US district court in New York, accused Rajat and Jayant Agarwalla - two software developers based in Calcutta - of violating Hasbro's copyright and trademarks. Facebook was not named as a defendant.

Neither brother nor any representative from their web design company, RJ Softwares, could immediately be reached for comment today.

At the time Hasbro launched its version of the game, Jayant Agarwalla told Times Online: "We strongly believe that people should have the option of playing what they like, rather than be forced by developers into using something they offer only for monetary gains."

The Agarwalla brothers have said they earn $25,000 (£13,000) a month from advertising on the application.

Facebook, which has so far refused to take down the game, said in a statement: "Over the past year, Facebook has tried to use its status as neutral platform provider to help the parties come to an amicable agreement. We’re disappointed that Hasbro has sought to draw us into their dispute."

By waiting, Facebook risks losing the protection it enjoys under US law, where online platforms are immune from legal actions by copyright owners as long as they take down offending content when notified.

In January, Mattel, the toymaker which owns the rights to Scrabble outside the US, wrote to Facebook asking it to take down the Scrabulous application, saying it valued its intellectual property and "actively protected" its brands and trademarks.

Within hours of the news breaking, thousands of players joined a "Save Scrabulous" group on Facebook, many of them claiming that Scrabulous had contributed to a renewed popularity of the game. Mattel has so far not followed up its demand.

The Association of British Scrabble Players has said that nothing has done more to get young people interested in playing Scrabble in the past five years than the Scrabulous application on Facebook.

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