Microsoft reported that hackers sponsored by the Russian government, who had been spying on the company’s executives earlier this year, had also stolen the source code. The company announced this in a new blog post.

The company did not specify what code was stolen. However, the company informs that the hacker group is now trying to use the stolen code to gain even more access to the software and customer data.

The attack was reportedly carried out by the Midnight Blizzard group, a Russian organization also known as Nobelium. Its members gained access to the code through emails between Microsoft and customers.

“In recent weeks, we have seen evidence that Midnight Blizzard is using information initially exfiltrated from our corporate email systems to gain, or attempt to gain, unauthorized access. This has included access to some of the company’s source code repositories and internal systems. To date we have found no evidence that Microsoft-hosted customer-facing systems have been compromised,” the blog post says.

The company is now also warning customers about the potential threat and urging them to take all protective measures. For its part, Microsoft is expanding its own capabilities to protect against future attacks.