A Chinese hacking group that has attacked U.S. and European aerospace and communications companies is almost certainly linked to the Chinese military, a U.S. Internet security company said Monday. "Putter Panda" has been active for several years, and a trail of Internet postings and domain registrations by one of its members points to it being part of Unit 61486 of China's People's Liberation Army, said Irvine, California-based CrowdStrike in a 62-page report.