Updated

The companies that make Scrabble are trying to shut down Scrabulous, an online version of the game that is one of the most popular applications on the social networking site Facebook.

Hasbro Inc., which owns the rights to the crossword game in the U.S. and Canada, and El Segundo, Calif.-based Mattel Inc., — which owns the rights elsewhere — believe the Facebook game infringes their copyrights and trademarks.

Scrabulous listed more than 600,000 daily active users on Facebook as of Wednesday and is one of the 10 most used applications on the site. People can also play at Scrabulous.com.

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The companies jointly issued cease-and-desist notices to four parties involved in the development, hosting and marketing of Scrabulous, according to a letter the Pawtucket-based Hasbro, Inc. is sending consumers who have contacted them about the game.

In a separate written statement released Wednesday, Hasbro was not specific about who the four parties are, but said it was reviewing a number of options with them and hoped to find an amicable solution.

"If we cannot come to one quickly, we will be forced to close down the site and its associated distribution points," Hasbro said.

Facebook and Scrabulous did not immediately return several requests for comment.

While there are authorized Scrabble games online, Scrabulous has gained popularity because it's free, easy to play with friends and easy to access on Facebook.

The game was developed by brothers Rajat and Jayant Agarwalla, from Calcutta, India, who say ,on the Web site, that they created it after they couldn't find an online version of Scrabble that they liked.

News of the toy companies' action prompted Scrabulous fans to start a "Save Scrabulous" group on Facebook and urge others to lodge protests with the companies by posting Web links to the Hasbro and Mattel sites.

In the letter Hasbro is sending to those who protest, the company urges Scrabulous fans to switch to legal Scrabble sites.

"We are not surprised that fans have thoroughly enjoyed playing Scrabulous on Facebook.com," the letter says. "What consumers may not realize, however, is that Scrabulous is an illegally copied online version of the world's most popular word game."

John D. Williams Jr., executive director of the National Scrabble Association, said the group was hopeful the companies could work out some sort of agreement. While most competitive Scrabble players don't play Scrabulous, he said the online game was a great way to introduce young people to the traditional board game.

"We're thrilled over anything that gets people playing more Scrabble," he said. "Our goal is to recruit them from the Internet and get them playing on a Scrabble board with a person sitting across from them."