Conventional wisdom about the sources and causes of denial-of-service (DOS) attacks — and the best methods for preventing them — could be completely wrong, a group of researchers said this week. Researchers at the University of Michigan, Carnegie Mellon University, and AT&T Labs-Research said they have completed a study that debunks the widely-held belief that DOS attack traffic is usually generated by a large number of attack sources disguised by spoofed IP addresses. In its study, the group found that 70 percent of DOS attacks are generated by less than 50 sources, and a relatively small number of attack sources account for nearly 72 percent of total attack volume.