Microsoft announced on Friday that Russian government hackers, known as Midnight Blizzard, continue to infiltrate the company’s systems in an ongoing attack, targeting the company’s source code and internal systems.

According to the tech giant, the hackers are using information obtained from corporate email systems to gain unauthorized access.

Microsoft also disclosed these new findings in a filing with the U.S. Securities and Exchange Commission on Friday.

The intrusion follows Microsoft’s disclosure in January that Russian hackers breached the company’s systems in November of the previous year, focusing on corporate email accounts of senior leadership and employees in cybersecurity, legal, and other functions.

Midnight Blizzard, also known as APT29 or Cozy Bear, has been able to gain access to various secrets obtained through emails shared between Microsoft and its customers. The group has been seen escalating its attempts to brute force accounts, commonly known as “password spraying,” indicating a sustained and significant commitment of resources and focus.

Microsoft warns that Midnight Blizzard may be accumulating information to enhance its ability to target specific areas.

The hacking group is believed to work for Russia’s Foreign Intelligence Service (SVR), and it has targeted high-profile entities over the years, including the Democratic National Committee in 2016 and SolarWinds in 2019. This indicates that the group has been involved in cyber espionage activities for some time now and has been successful in carrying out its attacks.

Microsoft has urged its customers to remain vigilant and take the necessary steps to protect themselves from cyber threats. The company has also assured that it is working tirelessly to defend against the ongoing attacks and has taken appropriate measures to secure its systems.