According to tech giant Microsoft, state-backed Russian hackers broke into its corporate email system and accessed the accounts of members of the company’s senior leadership team, as well as those of legal and cybersecurity employees.

In a blog post on Friday, Microsoft said the intrusion began in late November and was discovered on January 12.

The company noted that a very small amount of Microsoft corporate accounts were accessed and some emails and documents were stolen.

There was no immediate comment from Microsoft on which or how many members of the company’s senior leadership had their email accounts compromised.