A group of researchers at the Massachusetts Institute of Technology edged out about 4,300 other teams on Saturday in a Pentagon-sponsored contest to correctly identify the location of 10 red balloons distributed around the United States.

The contest, which featured a $40,000 prize, was organized by the Defense Advanced Research Projects Agency, in an effort to develop new ways to understand how information is disseminated through social networks.

The winning group, a small team at the MIT Media Laboratory Human Dynamics Group led by a physicist, Riley Crane, took just eight hours and 56 minutes to complete the challenge.

The balloons, which were 8 feet in diameter, were arrayed around the country. Some were in highly trafficked locations like Union Square in San Francisco; others were in more obscure places, like Katy Park, a baseball field in the Houston suburbs.

The winning researchers, who specialize in studying human interactions that emerge from computer networks, set up a Web site asking people to join their team. They relied on visitors to the Web site to invite their friends. They also sent e-mail messages inviting people to participate and sent a small number of advertisements to mobile phones.

They said that they would dole out the prize money both to chains of individuals who referred people who had correct information on the balloons' locations and to charities. They described their method as a “;recursive incentive structure.”;

The approach “;rewards people who make real contributions,”; said Crane, whose research has recently focused on how information spreads in computer networks, like YouTube.

“;This was a once-in-a-lifetime opportunity to perform an experiment at a massive scale,”; he said.

In the simplest case, a single person who contributed the correct answer would be given $2,000 and the research group would give another $2,000 to charity. In cases where multiple people contributed, participants will get some fraction of $4,000.

The researchers said they had received contributions from 4,665 participants.

“;They got a huge amount of participation from shockingly little money,”; said Peter Lee, a DARPA project manager who was one of the organizers of the Network Challenge.

DARPA had begun holding similar events focused on autonomous vehicles in 2004 to create incentives to quickly advance the state-of-the-art. In the Network Challenge roughly 500 teams had made a serious effort and come close to identifying all of the balloons in a contest that Lee referred to as a “;nail-biter.”;

He said while they were planning the event the DARPA scientists had wondered about the relative effectiveness of different motives ranging from profit to working for the common good.

“;In the final results all of the motives seemed to be effective,”; he said.

The researchers said their technique could be used for many things, including finding criminals and missing children, and halting impending terrorist attacks.