Big data — the collection and analysis of enormous amounts of information by supercomputers — is leading to huge advances in such fields as astrophysics, medicine, social science, business and crime fighting. And big data is growing exponentially: According to IBM, 90 percent of the world's data has been generated within just the past two years. But the use of big data — including Tweets, Facebook images and email addresses — is controversial because of its potential to erode individual privacy, especially by governments conducting surveillance operations and companies marketing products. Some civil liberties advocates want to control the use of big data, and others think companies should pay to use people's online information. But some proponents of big data say the benefits outweigh the risks and that privacy is an outdated concept.