The Web site Free Rice is getting a lot of attention this week, but at least one blog writer is offering a word of caution about the hype.

The site tests users’ vocabulary skills and offers grains of rice to the United Nations World Fund program for every answer a user gets correct.

But the site isn’t just a philanthropic exercise.

It’s a moneymaker for its creator.

“Sad thing is, it’s actually a vocabulary test masking as an ad server, while the rice you donate does seem to go to the UN World Food Program,” writes Lucy Bernholz, the author of the blog Philanthropy 2173. “The real money is in the ad clicks — companies support the site, you click on their ads, they pay the Web site for the click.”

Whenever a visitor to the site gets a correct answer to a vocabulary question, he or she is taken to a new page that includes the next question — and several ads for companies such as Apple, American Express, and Liz Claiborne.

The concept is clever, but Ms. Bernholz, a strategy consultant for nonprofit groups and foundations, says visitors should understand that it’s not a charitable venture.

Her message: “Beware — embedded giving is not always what it seems.”

What do you think about this effort? Is this an online twist on cause marketing that will work — or will it turn off potential donors?