The hackers who carried out the attack at SolarWinds 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 source repositories code the company's.
The news came from the company itself on Thursday.
Microsoft said the attackers did not make changes to the repositories they accessed because the compromised accounts they only had rights to view the code.
The company stressed that, despite displaying some points of the source code, hackers were unable to gain access to production systems, customer data or 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 they discovered malicious software on their networks, which 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 the confidentiality of the source code for the better safety of products and the security models we use assume that attackers already know the source code.”