78 COMMUNICATIONS OF THE ACM | APRIL 2011 | VOL. 54 | NO. 4 contributed articles PHOTOGRAPH COURTESY OF DARPA THE 2009 DARPA Red Balloon Challenge (also known as the DARPA Network Challenge) explored how the Internet and social networking can be used to solve a distributed, time-critical, geo-location problem. Teams had to ind 10 red weather balloons deployed at undisclosed locations across the continental U.S. The irst team to correctly identify the locations of all 10 would win a $40,000 prize. A team from the Massachusetts Institute of Technology (MIT) won in less than nine hours (http://networkchallenge.darpa. mil/). Here, we relect on lessons learned from the strategies used by the various teams. The Challenge commemorated the 40 th anniversary of the irst remote log-in to the ARPANet (October 29, 1969), an event widely heralded as the birth of the Internet. The Challenge was designed to identify Relecting on the DARPA Red Balloon Challenge DOI:10.1145/1924421.1924441 Finding 10 balloons across the U.S. illustrates how the Internet has changed the way we solve highly distributed problems. BY JOHN C. TANG, MANUEL CEBRIAN, NICKLAUS A. GIACOBE, HYUN-WOO KIM, TAEMIE KIM, AND DOUGLAS “BEAKER” WICKERT how more recent developments (such as social media and crowdsourcing) could be used to solve challenging problems involving distributed geo- locations. Since the Challenge was an- nounced only about one month before the balloons were deployed, it was not only a timed contest to ind the bal- loons but also a time-limited challenge to prepare for the contest. Both the dif- fusion of how teams heard about the Challenge and the solution itself dem- onstrated the relative effectiveness of mass media and social media. The surprising eficiency of apply- ing social networks of acquaintances to solve widely distributed tasks was demonstrated in Stanley Milgram’s celebrated work 9 popularizing the no- tion of “six degrees of separation”; that is, it typically takes no more than six in- termediaries to connect any arbitrary pair of people. Meanwhile, the Internet and other communication technolo- gies have emerged that increase the ease and opportunity for connections. These developments have enabled crowdsourcing—aggregating bits of information across a large number of users to create productive value—as a popular mechanism for creating en- cyclopedias of information (such as Wikipedia) and solving other highly distributed problems. 1 The Challenge was announced at the “40th Anniversary of the Internet” event (http://www.engineer.ucla.edu/IA40/ index.html). On December 5, 2009, at 10:00 a.m. Eastern time, 10 numbered, eight-foot-diameter red weather bal- loons were deployed at moored loca- key insights Crowdsourcing, social networking, and traditional media enabled teams to quickly find 10 weather balloons scattered across the U.S. Besides finding the balloons, distinguishing correct balloon sightings from misleading claims turned out to be an important part of the effort. Variations in the strategies of the competing teams reflected differences in how social media can be tailored to fit a given task.