Stepping up a feud with Washington over technology and security, China’s government on Sunday told users of computer equipment deemed sensitive to stop buying products from the biggest U.S. memory chipmaker, Micron Technology Inc. Micron products have unspecified “serious network security risks” that pose hazards to China’s information infrastructure and affect national security, the Cyberspace Administration of China said on its website. Its six-sentence statement gave no details. “Operators of critical information infrastructure in China should stop purchasing products from Micron Co.,” the agency said. The United States, Europe and Japan are reducing Chinese access to advanced chipmaking and other...