The hackers who carried out the SolarWinds attack were able to gain access to Microsoft's internal network and gain access to a small number of internal accounts, which were used to access the company's source code repositories.
The news came from the company itself on Thursday.
Microsoft said the attackers did not make any changes to the accessed repositories because the compromised accounts were only allowed to display the code.
The company stressed that, despite viewing parts of the source code, the hackers were unable to reach systems production, customer data or obtain Microsoft products to attack the company's customers.
The Redmond-based company says its investigation is ongoing.
Microsoft admitted on December 17 that it was using SolarWinds Orion, a monitoring platform, within its network.
It was one of thousands of companies that discovered malware on their networks that were created through infected Orion updates.
Of course, Microsoft denies that the hackers saw the internal source code repositories, claiming that this is not important.
"At Microsoft, we have an internal source approach - we use best open source software development practices.
This means that we do not rely on source code confidentiality for product security and models security that we use assume that attackers already know the source code.”