Suspected Chinese hackers are behind an ongoing cyberespionage campaign against US technology companies and legal firms, stealing national security secrets often while remaining undetected, according to Alphabet Inc.’s Google.The hacking group, which Google tracks under the code name UNC5221, are “the most prevalent adversary in the US over the past several years” in terms of frequency, severity and complexity of incidents, said Charles Carmakal, chief technology officer at Google Cloud’s Mandiant consultin ...