Microsoft Corp stated that a Chinese hacking group thought to have government backing is targeting previously unknown security flaws in an email product used by businesses. The company announced on Tuesday that the group, which it calls “Hafnium,” is targeting vulnerabilities in versions of Exchange Server, an email and calendar application, that run on computer systems in physical offices. Hafnium previously attempted to steal information from infectious disease researchers, law firms, defense contractors and others, Microsoft said.Microsoft urged clients to update their Exchange Server to patch four vulnerabilities and warned of spinoff attacks. Researchers at Microsoft attributed the activity, which they are discussing publicly for the first time, to a state-sponsored Chinese group with a high degree of confidence based on its tactics. The Chinese Embassy in Washington didn’t immediately respond to a request for comment.