Russian hackers breached Microsoft systems earlier this year, stealing emails from Microsoft staff and its customers, according to the tech giant. The disclosure highlights the extensive scope of the breach, adding to the regulatory scrutiny Microsoft faces over the security of its software and systems. The hackers, identified as the Midnight Blizzard threat actor, targeted cybersecurity researchers investigating Russian hacking activities.

Microsoft has been notifying affected customers, although the company has not disclosed the number of customers or emails impacted. Initially revealed in January as affecting a small percentage of corporate email accounts, the breach continued to pose threats for months, raising concerns among the security industry and prompting a Congressional hearing. In response, Microsoft President Brad Smith stated the company is working on overhauling its security practices.