Players can spend the points at the P.M.O.G. shop, buying treasure, mines (right), portals, or other game pieces to leave on websites for others to find—if they, too, have downloaded the software. Game designers said players could bomb each other, wage war over websites, and lead other users on Web missions.

"It's about building social games across the internet by using the internet itself," says Hall, from Oakland, California, where GameLayers is based.

The idea was intriguing enough to attract seed money from former RealNetworks executive Richard Wolpert, O'Reilly AlphaTech Ventures, and longtime friend Ito, the C.E.O. of Creative Commons who has scored as an angel investor in several fairly well-known Web 2.0 properties, including Last.fm and Technorati.

As the number of players grew, Hall and his partners faced a familiar problem: how to turn their game into a business.

In P.M.O.G., this might mean allowing advertisers to attach their names to parts of the game, such as the badges that players earn for accomplishing certain tasks or learning skills. (There is a Torch badge for visiting 100 URLs in 24 hours, for example, and a Queen Bee for hitting Perez Hilton's Hollywood gossip site five days a week for two weeks.)

Hall, Grace, and Gough say companies have approached them to build branded badges and missions since the game's test version went up in January. For good reason: Players are passionate about badges. When a glitch delayed the award of some badges last week, itchy users lit up user forums with complaints.

But there are daunting hurdles yet to clear.

One is a critical mass of users, one big enough to reliably attract advertisers. A widely accepted benchmark is one million players: a far cry from the 25,000 now signed up to P.M.O.G.

Another is finding sponsors that fit the context of the game: P.M.O.G.'s pseudo-Victorian setting may not mesh with an S.U.V. ad, for instance.

A third issue is privacy. Web users have complained about efforts by Google and DoubleClick to compile surfing histories; will they be any less worried about a game that tracks their Web habits?

"The biggest fear, next to people not playing it, is that users' first thoughts will be where is this data going," Ito says. "We're going to have to have a policy on how we collect and preserve data, and I don't think we're there yet."

Finally, there is the problem of whether ads will alienate players. The P.M.O.G. community is already showing signs of skepticism. As players race to accrue badges, some are asking if the rewards are, in fact, ad-sponsored. "Do you think people pay to have their site become a badge?" asked a player tagged Mosler.

Grace says no. For now, she says, badges are picked because they represent the co-founders favorite sites. But future investors will want commerce to trump the quirky, especially as the company has already burned through $500,000 in seed money and is seeking additional funding.

Grace, Hall, and Gough stress that, on this point, they'll take their cues from users. For now, at least, that's good enough for Ito, P.M.O.G.'s biggest cheerleader. He says he believes if they build a brand and attract users, a business will follow.

"People make fun of the idea of having lots of users but no business model," Ito says. "There are few sites, however, that have a critical mass where they usually don't figure out a business model. And I've never been wrong with that."