More: Viral marketing, the compelling game, and the cause it supports are key to the site's success, WFP's Barton says.

An ad is featured on the bottom of each page, and it is these advertisers who ultimately fund the checks Breen writes to the WFP. He is looking into Google ads and hiring an ad agency to run the site. Breen has specified that he wants the WFP to buy locally to support farmers in developing countries, rather than using imported food, which tends to depress local crop prices.

Breen has already sent $113,000 to the WFP and will send more in increments of $10,000 to $15,000 as advertising dollars roll in, Barton says. Breen says he sends all profits to the WFP, and the site has no political or religious affiliation. He donates his time and pays the cost of leasing the site's servers himself. "Some people like to give money to their colleges or whatever," he writes by e-mail, "and this I what I prefer to do with it."