The web-based social game Mafia Wars attracts 4 million daily users one year after debuting on social networking sites, developer Zynga said Thursday.

The game launched in June 2008, and according to Zynga, doubled the number of daily players in the last three months. The game, available on sites such as Facebook, MySpace, Tagged, and Yahoo, also launched in iPhone in April this year.

Mafia Wars lets players start a mob family with their friends and run crime businesses. At four million daily users, the game makes up a third of Zynga's daily traffic across all of its games, which totals 12 million daily users.

Zynga claims to attract 50 million daily users per month, and the game, which is initially free to play, monetizes itself by allowing players to pay for extra items and resources via micropayments.

“Mafia Wars is on its way to becoming a cult classic,” claimed Zynga's Bill Mooney, executive producer.

In May, Zynga opened a Baltimore, Maryland-based studio, Zynga East, led by chief designer Brian Reynolds, best known for strategy games including Civilization II, Alpha Centauri, and Rise of Nations.