Players who use computers to cheat are a growing concern in the chess world. Now the developer of Rybka, the winner of the last four World Computer Chess Championships, has been accused of plagiarizing code to create the program.

Rybka has been stripped of its titles, and the developer, Vasik Rajlich, has been barred from entering programs in competitions.

The ruling on Rybka and Mr. Rajlich was made Tuesday by the International Computer Gaming Association, the group that organizes the championships. It concluded that Mr. Rajlich, who has American and Czech citizenship and lives in Poland, had used source code from programs called Crafty and Fruit.

“We are convinced that the evidence against Vasik Rajlich is both overwhelming in its volume and beyond reasonable question in its nature,” the association’s executive committee said in a statement.