US Treasury Secretary Janet Yellen’s computer was infiltrated and unclassified files were accessed as part of a broader breach of the agency by Chinese state-sponsored hackers, according to two people familiar with the matter. The attackers also hacked the computers of two of Yellen’s lieutenants, Deputy Secretary Wally Adeyemo and Acting Under Secretary Brad Smith, according to the people, who asked not to be identified discussing sensitive information. Fewer than 50 files on Yellen’s machine w...