Before he became the new face of right-wing extremism in Europe, Anders Behring Breivik was just another guy airing his anti-immigration views online. On Monday, Breivik, who admitted to a killing spree in Norway in July, which left 77 people dead, faced his first public-court hearing. While Breivik may have acted alone, he was far from alone in cyberspace: he had spent much of the time leading up to his attack at his computer, chatting with some of the millions of nationalists who support right-wing groups on social-networking sites. After this summer's tragedy, researchers wanted to find out more about these people. But how to find them? Easy  just log on to Facebook.  "We realized that it wasn't that difficult to get to them at all," says Jamie Bartlett, the lead author of a recently published report on European digital populism by British think tank Demos. Facebook's stash of personal information is so encyclopedic, says Bartlett, that the researchers could simply use the site's advertising tool to pinpoint their desired demographic with scientific accuracy  the way marketers have been doing for years. Bartlett's team found half a million fans of right-wing groups across Europe and then targeted them with ads, but instead of linking to a new band or diet product, the ads invited users to complete a survey that asked questions about their education level, attitudes toward violence and optimism about their own future. (Read about Facebook's privacy features.)  By reaching out through Facebook, Bartlett and his colleagues were able to survey over 10,000 followers of 14 far-right parties in 11 European countries  all without ever leaving the office. "It's quite a new way of doing research," Bartlett says. Some of the results aren't all that surprising: online supporters of right-wing groups tend to be young, male and vexed by immigration. But in something of a twist, "those who combine their online activism with off-line activism are more reasonable, more democratic and less violent than those who just remain behind the computer screen."  Demos' work is just one example of how Facebook is becoming a hot new tool in the hands of scientists. Think tanks, medical researchers and political scientists are using the site to study everything from health issues to social trends as expressed in Likes, Wall posts and Status Updates. With over 800 million active users adding an average of three pieces of content per day, the Facebook "data supernova" is generating a research boom, driving the number of academic papers with the site's name in the title up almost 800% over the past five years.  For some researchers, the beauty of Facebook is that it lets you study people you couldn't approach with a clipboard on the street. "Before, when you tried to survey people from the British National Party, it would be very difficult to identify them. You'd have to go through the party, and they would never allow you access," says Bartlett. "Facebook cuts all that out  you go to them directly."  Others say the site could offer a way to identify and tackle social-health problems. A recent study by Dr. Megan Moreno, of the University of Wisconsin-Madison, and her colleagues found that undergraduates who discussed their drunken exploits on Facebook were significantly more at risk for problem drinking than students who were silent on the topic. Moreno suggests that students' peers, like residential advisers, could monitor the site and intervene to help a student who posts one too many boozy Status Updates. "You can't treat a problem if you can't diagnose it," Dimitri Christakis, Moreno's co-author and director of the Center for Child Health, Behavior and Development at Seattle Children's Research Institute, told the Washington Post. "We've found a way to identify kids at risk who would not otherwise be diagnosed." (See the 10 things you shouldn't do on Facebook.)  Facebook, too, is constantly tapping into its own population for data. The site's Data Team has worked up stats on relationship status and Valentine's Day; voter turnout in the 2010 midterms; and a National Happiness Index (mainly using information that only it can access  champions of digital freedom have long held that the site should make its vast trove of data available to others for research). But Facebook's users know the site is watching them, whether they like it or not  the trade-off for being able to play Scrabble with a friend thousands of miles away is allowing the site to mine your personal information.  But what about when Facebook users become part of a survey they don't even know about? While researchers have well-defined guidelines about how they collect their data off-line, online it's a free-for-all. "I don't think a lot of [users] had even thought about the fact that a researcher could be looking at their profiles," says Neil Selwyn, a sociologist at the London Knowledge Lab, of a 2006 study he conducted using students' public Facebook Walls. "As far as they were concerned, it was just between them and their friends."  Then there's the question of methodology. Even off-line, there's no guarantee that a research subject is being completely honest. On Facebook, it's impossible to know how much of a user's profile information and Wall posts are true. "What you say on Facebook and what you do outside of Facebook are two completely different things," says Selwyn. (Read about Facebook users' thoughts on the social-networking site.)  Which is why, despite his years as a technology researcher, Selwyn thinks a clipboard and a pen are still the best research tools anyone can use. "There's no substitute for going into the real world and speaking to real people," he says. "Social research is supposed to be about the social  and a hell of a lot of the social still takes place offline."  Watch TIME's video on how people of all ages are connecting through Facebook.  Read about Mark Zuckerberg, who was named TIME's 2010 Person of the Year.
Advertisers aren't the only ones exploiting social-networking sites -- now scientists are tapping into Facebook's trove of personal data to find lab rats online