BREA, Calif. — The front line in the battle to protect U.S. critical infrastructure ran this month through a rental house in Orange County.More than a dozen hackers from Arizona State University, the University of California-Santa Barbara and Purdue University tapped on laptops spread among tables, couches and the kitchen counter, looking over one another’s shoulders and sometimes asking peers or professors for help.The mission of the hackathon: to write a program that can scan millions of line...