Since its onset, online gambling has demonstrated consistently impressive growth and this is particularly evident in the last six months thanks, in part, to the resurgent fascination with the game of poker.

comScore Network’s gambling category of sites, attracted 29.13 million unique visitors in the month of April as compared with 25.43 million visitors last November. This amounts to a remarkable 14.5 percent increase in just a few months.

IGlobalMedia Entertainment’s network of sites, which includes PartyBingo.com, PartyPoker.com, and StarLuckCasino.com, attracted the most visitors in April with a total of 10.3 million visitors. That’s a 166 percent increase over last year’s figure for April, which was 3.89 million visitors. For those interested in using iGlobalMedia’s site, all they need to do is download the appropriate software and set up an account.

In spite of the rapid growth of poker sites, the parent companies of these poker sites have remained oddly silent about their success. In fact, iGlobalMedia’s corporate site lists only email addresses. No phone numbers are provided. Live agents at PartyPoker.com’s customer service center, located in India, will answer your calls but will politely decline any requests for corporate contact information.

Their hesitancy to publicize this information is probably due to the question of legality that surrounds the whole Internet gambling industry. The Internet gambling issue, in fact, has become an international problem especially since the WTO’s ruling that the U.S. Internet gambling policy violates international free trade rules to which the U.S. is a party. Of comScore’s top 15 gambling sites, all but two, iWin.com and FreeSlots.com, are based outside of the U.S.

Still, poker sites are not averse to advertising their services in spite of the ongoing question of legality. Some sites have been running television advertisements that feature endorsements from well-known American players. Indeed, World Series of Poker Champions, Chris Moneymaker and Greg Raymen, were featured on PokerStars.com, a London-based poker site. While the advertisements make it clear that Pokerstars.com is not a gambling site, a quick visit to the site demonstrates otherwise. The main page of the site advertises a weekly No Limit Texas Hold Em tournament with a guaranteed minimum prize pool of $350,000.