"Just at the moment, with the upsurge of interest, I am getting three or four enquiries from around the world a day so it won't be long before it is everywhere," he predicted.
The brain teaser comes in different levels from easy, which can take up to an hour to crack, to fiendish, which often proves too difficult to solve, resulting in the dreaded moment when a player realizes he or she has repeated a number in one of the lines or boxes and has to back-track or start again.
"If you get it wrong it is really frustrating," said Nicholas Webb, a London lawyer who has been hooked on Sudoku since it first appeared in The Times.
At the same time, the 28-year-old who "Sudokus" regularly on the bus to work, said, "There is a great feeling of satisfaction when you finish one of them."
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