SAN JOSE (AP) — Security researcher Brian Wallace was on the trail of hackers who had snatched a California university’s housing files when he stumbled into a larger nightmare: Cyberattackers had opened a pathway into the networks running the United States’ power grid.Digital clues pointed to Iranian hackers. And Wallace found that they had already taken passwords, as well as engineering drawings of dozens of power plants, at least one with the title “Mission Critical.” The drawings were so detailed that experts say skilled attackers could have used them, along with other tools and malicious code, to knock out electricity flowing to millions of homes.Wallace was astonished.