The U.S. Department of Homeland Security on Friday advised owners of Lenovo computers to remove a software program known as “Superfish,” which it said the world’s No. 1 PC maker started installing on some machines as early as 2010. Homeland Security said in an alert released through its National Cyber Awareness System that the software made users vulnerable to a type of cyberattack known as SSL spoofing. “Systems that came with the software already installed will continue to be vulnerable until corrective actions have been taken,” the agency said.