The category attracted 87 million US visitors in May 2009, up 22 per cent compared to the prior year, as users opted for cheaper entertainment alternatives driven by current economic crisis, says the report.

Yahoo! Games has been rated as number one site, attracting 19.4 million visitors, and representing a six per cent increase to that of last year. It is followed by EA Online with 18 million visitors, Nickelodeon Casual Games with 14.8 million visitors and WildTangent Network with 13.8 million.

Among others, GSN Games Networks managed to bring in six million users with its newly created WorldWinner.com and CrazyMonkey.com, taking its growth to 563 per cent.

"Online gaming continues to be one of the top gaining categories over the last year growing at ten times the rate of the total US Internet population and reaching nearly one out of every two Internet users," said comScore director - gaming solutions Edward Hunter. "The growth in the category is occurring not only at the top gaming destination sites but also through viral distribution platforms, including widgets and applications. In fact, some online gaming companies that distributed their games across sites are reaching as many people as the top online gaming sites," adds Hunter