Russian hackers compromised Microsoft cloud customers through third party, putting emails and other data at risk

Russian government hackers have compromised Microsoft cloud customers and stolen emails from at least one private-sector company, according to people familiar with the matter, a worrying development in Moscow’s ongoing cyberespionage campaign targeting numerous U.S. agencies and corporate computer networks.

The intrusions appear to have occurred via a Microsoft corporate partner that handles cloud-access services, those familiar with the matter said. They did not identify the partner or the company known to have had emails stolen. Like others, these people spoke on the condition of anonymity to discuss what remains a highly sensitive subject.